import unittest
# from test import support
from itertools import *
# import weakref
# from decimal import Decimal
# from fractions import Fraction
import operator
# import random
import copy
# import pickle
from functools import reduce
import sys
# import struct
# import threading
# maxsize = support.MAX_Py_ssize_t
# minsize = -maxsize-1
maxsize = int(sys.maxsize**.5) # maxsize is too large to handle!
minsize = -maxsize-1

def lzip(*args):
    return list(zip(*args))

def onearg(x):
    'Test function of one argument'
    return 2*x

def errfunc(*args):
    'Test function that raises an error'
    raise ValueError

def gen3():
    'Non-restartable source sequence'
    for i in (0, 1, 2):
        yield i

def isEven(x):
    'Test predicate'
    return x%2==0

def isOdd(x):
    'Test predicate'
    return x%2==1

def tupleize(*args):
    return args

def irange(n):
    for i in range(n):
        yield i

class StopNow:
    'Class emulating an empty iterable.'
    def __iter__(self):
        return self
    def __next__(self):
        raise StopIteration

def take(n, seq):
    'Convenience function for partially consuming a long of infinite iterable'
    return list(islice(seq, n))

def prod(iterable):
    return reduce(operator.mul, iterable, 1)

def fact(n):
    'Factorial'
    return prod(range(1, n+1))

# root level methods for pickling ability
def testR(r):
    return r[0]

def testR2(r):
    return r[2]

def underten(x):
    return x<10

# picklecopiers = [lambda s, proto=proto: pickle.loads(pickle.dumps(s, proto))
#                  for proto in range(pickle.HIGHEST_PROTOCOL + 1)]

class TestBasicOps(unittest.TestCase):
    pass

#     def pickletest(self, protocol, it, stop=4, take=1, compare=None):
#         """Test that an iterator is the same after pickling, also when part-consumed"""
#         def expand(it, i=0):
#             # Recursively expand iterables, within sensible bounds
#             if i > 10:
#                 raise RuntimeError("infinite recursion encountered")
#             if isinstance(it, str):
#                 return it
#             try:
#                 l = list(islice(it, stop))
#             except TypeError:
#                 return it # can't expand it
#             return [expand(e, i+1) for e in l]

#         # Test the initial copy against the original
#         dump = pickle.dumps(it, protocol)
#         i2 = pickle.loads(dump)
#         self.assertEqual(type(it), type(i2))
#         a, b = expand(it), expand(i2)
#         self.assertEqual(a, b)
#         if compare:
#             c = expand(compare)
#             self.assertEqual(a, c)

#         # Take from the copy, and create another copy and compare them.
#         i3 = pickle.loads(dump)
#         took = 0
#         try:
#             for i in range(take):
#                 next(i3)
#                 took += 1
#         except StopIteration:
#             pass #in case there is less data than 'take'
#         dump = pickle.dumps(i3, protocol)
#         i4 = pickle.loads(dump)
#         a, b = expand(i3), expand(i4)
#         self.assertEqual(a, b)
#         if compare:
#             c = expand(compare[took:])
#             self.assertEqual(a, c);

    def test_accumulate(self):
        self.assertEqual(list(accumulate(range(10))),               # one positional arg
                          [0, 1, 3, 6, 10, 15, 21, 28, 36, 45])
        self.assertEqual(list(accumulate(iterable=range(10))),      # kw arg
                          [0, 1, 3, 6, 10, 15, 21, 28, 36, 45])
        for typ in int, complex: #, Decimal, Fraction:                 # multiple types
            self.assertEqual(
                list(accumulate(map(typ, range(10)))),
                list(map(typ, [0, 1, 3, 6, 10, 15, 21, 28, 36, 45])))
        self.assertEqual(list(accumulate('abc')), ['a', 'ab', 'abc'])   # works with non-numeric
        self.assertEqual(list(accumulate([])), [])                  # empty iterable
        self.assertEqual(list(accumulate([7])), [7])                # iterable of length one
        self.assertRaises(TypeError, accumulate, range(10), 5, 6)   # too many args
        self.assertRaises(TypeError, accumulate)                    # too few args
        # self.assertRaises(TypeError, accumulate, x=range(10))       # unexpected kwd arg
        self.assertRaises(TypeError, list, accumulate([1, []]))     # args that don't add

        s = [2, 8, 9, 5, 7, 0, 3, 4, 1, 6]
        self.assertEqual(list(accumulate(s, min)),
                         [2, 2, 2, 2, 2, 0, 0, 0, 0, 0])
        self.assertEqual(list(accumulate(s, max)),
                         [2, 8, 9, 9, 9, 9, 9, 9, 9, 9])
        self.assertEqual(list(accumulate(s, operator.mul)),
                         [2, 16, 144, 720, 5040, 0, 0, 0, 0, 0])
        self.assertEqual(list(accumulate([10, 5, 1], initial=None)), [10, 15, 16])
        self.assertEqual(list(accumulate([10, 5, 1], initial=100)), [100, 110, 115, 116])
        self.assertEqual(list(accumulate([], initial=100)), [100])
        self.assertRaises(TypeError, list, accumulate(s, chr))                                # unary-operation
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             self.pickletest(proto, accumulate(range(10)))           # test pickling

    def test_chain(self):

        # def chain2(*iterables):
        #     'Pure python version in the docs'
        #     for it in iterables:
        #         for element in it:
        #             yield element

        for c in (chain,):# chain2):
            self.assertEqual(list(c('abc', 'def')), list('abcdef'))
            self.assertEqual(list(c('abc')), list('abc'))
            self.assertEqual(list(c('')), [])
            self.assertEqual(take(4, c('abc', 'def')), list('abcd'))
            self.assertRaises(TypeError, list,c(2, 3))

    def test_chain_from_iterable(self):
        self.assertEqual(list(chain.from_iterable(['abc', 'def'])), list('abcdef'))
        self.assertEqual(list(chain.from_iterable(['abc'])), list('abc'))
        self.assertEqual(list(chain.from_iterable([''])), [])
        self.assertEqual(take(4, chain.from_iterable(['abc', 'def'])), list('abcd'))
        self.assertRaises(TypeError, list, chain.from_iterable([2, 3]))

#     def test_chain_reducible(self):
#         for oper in [copy.deepcopy] + picklecopiers:
#             it = chain('abc', 'def')
#             self.assertEqual(list(oper(it)), list('abcdef'))
#             self.assertEqual(next(it), 'a')
#             self.assertEqual(list(oper(it)), list('bcdef'))

#             self.assertEqual(list(oper(chain(''))), [])
#             self.assertEqual(take(4, oper(chain('abc', 'def'))), list('abcd'))
#             self.assertRaises(TypeError, list, oper(chain(2, 3)))
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             self.pickletest(proto, chain('abc', 'def'), compare=list('abcdef'))

#     def test_chain_setstate(self):
#         self.assertRaises(TypeError, chain().__setstate__, ())
#         self.assertRaises(TypeError, chain().__setstate__, [])
#         self.assertRaises(TypeError, chain().__setstate__, 0)
#         self.assertRaises(TypeError, chain().__setstate__, ([],))
#         self.assertRaises(TypeError, chain().__setstate__, (iter([]), []))
#         it = chain()
#         it.__setstate__((iter(['abc', 'def']),))
#         self.assertEqual(list(it), ['a', 'b', 'c', 'd', 'e', 'f'])
#         it = chain()
#         it.__setstate__((iter(['abc', 'def']), iter(['ghi'])))
#         self.assertEqual(list(it), ['ghi', 'a', 'b', 'c', 'd', 'e', 'f'])

    def test_combinations(self):
        self.assertRaises(TypeError, combinations, 'abc')       # missing r argument
        self.assertRaises(TypeError, combinations, 'abc', 2, 1) # too many arguments
        self.assertRaises(TypeError, combinations, None)        # pool is not iterable
        self.assertRaises(ValueError, combinations, 'abc', -2)  # r is negative

#         for op in [lambda a:a] + picklecopiers:
#             self.assertEqual(list(op(combinations('abc', 32))), [])     # r > n

#             self.assertEqual(list(op(combinations('ABCD', 2))),
#                              [('A','B'), ('A','C'), ('A','D'), ('B','C'), ('B','D'), ('C','D')])
#             testIntermediate = combinations('ABCD', 2)
#             next(testIntermediate)
#             self.assertEqual(list(op(testIntermediate)),
#                              [('A','C'), ('A','D'), ('B','C'), ('B','D'), ('C','D')])

#             self.assertEqual(list(op(combinations(range(4), 3))),
#                              [(0,1,2), (0,1,3), (0,2,3), (1,2,3)])
#             testIntermediate = combinations(range(4), 3)
#             next(testIntermediate)
#             self.assertEqual(list(op(testIntermediate)),
#                              [(0,1,3), (0,2,3), (1,2,3)])


#         def combinations1(iterable, r):
#             'Pure python version shown in the docs'
#             pool = tuple(iterable)
#             n = len(pool)
#             if r > n:
#                 return
#             indices = list(range(r))
#             yield tuple(pool[i] for i in indices)
#             while 1:
#                 for i in reversed(range(r)):
#                     if indices[i] != i + n - r:
#                         break
#                 else:
#                     return
#                 indices[i] += 1
#                 for j in range(i+1, r):
#                     indices[j] = indices[j-1] + 1
#                 yield tuple(pool[i] for i in indices)

#         def combinations2(iterable, r):
#             'Pure python version shown in the docs'
#             pool = tuple(iterable)
#             n = len(pool)
#             for indices in permutations(range(n), r):
#                 if sorted(indices) == list(indices):
#                     yield tuple(pool[i] for i in indices)

#         def combinations3(iterable, r):
#             'Pure python version from cwr()'
#             pool = tuple(iterable)
#             n = len(pool)
#             for indices in combinations_with_replacement(range(n), r):
#                 if len(set(indices)) == r:
#                     yield tuple(pool[i] for i in indices)

        for n in range(7):
            values = [5*x-12 for x in range(n)]
            for r in range(n+2):
                result = list(combinations(values, r))
                self.assertEqual(len(result), 0 if r>n else fact(n) / fact(r) / fact(n-r)) # right number of combs
                self.assertEqual(len(result), len(set(result)))         # no repeats
                self.assertEqual(result, sorted(result))                # lexicographic order
                for c in result:
                    self.assertEqual(len(c), r)                         # r-length combinations
                    self.assertEqual(len(set(c)), r)                    # no duplicate elements
                    self.assertEqual(list(c), sorted(c))                # keep original ordering
                    self.assertTrue(all(e in values for e in c))           # elements taken from input iterable
                    self.assertEqual(list(c),
                                     [e for e in values if e in c])      # comb is a subsequence of the input iterable
#                 self.assertEqual(result, list(combinations1(values, r))) # matches first pure python version
#                 self.assertEqual(result, list(combinations2(values, r))) # matches second pure python version
#                 self.assertEqual(result, list(combinations3(values, r))) # matches second pure python version

#                 for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#                     self.pickletest(proto, combinations(values, r))      # test pickling

#     @support.bigaddrspacetest
#     def test_combinations_overflow(self):
#         with self.assertRaises((OverflowError, MemoryError)):
#             combinations("AA", 2**29)

#         # Test implementation detail:  tuple re-use
#     @support.impl_detail("tuple reuse is specific to CPython")
#     def test_combinations_tuple_reuse(self):
#         self.assertEqual(len(set(map(id, combinations('abcde', 3)))), 1)
#         self.assertNotEqual(len(set(map(id, list(combinations('abcde', 3))))), 1)

    def test_combinations_with_replacement(self):
        cwr = combinations_with_replacement
        self.assertRaises(TypeError, cwr, 'abc')       # missing r argument
        self.assertRaises(TypeError, cwr, 'abc', 2, 1) # too many arguments
        self.assertRaises(TypeError, cwr, None)        # pool is not iterable
        self.assertRaises(ValueError, cwr, 'abc', -2)  # r is negative

#         for op in [lambda a:a] + picklecopiers:
#             self.assertEqual(list(op(cwr('ABC', 2))),
#                              [('A','A'), ('A','B'), ('A','C'), ('B','B'), ('B','C'), ('C','C')])
#             testIntermediate = cwr('ABC', 2)
#             next(testIntermediate)
#             self.assertEqual(list(op(testIntermediate)),
#                              [('A','B'), ('A','C'), ('B','B'), ('B','C'), ('C','C')])


#         def cwr1(iterable, r):
#             'Pure python version shown in the docs'
#             # number items returned:  (n+r-1)! / r! / (n-1)! when n>0
#             pool = tuple(iterable)
#             n = len(pool)
#             if not n and r:
#                 return
#             indices = [0] * r
#             yield tuple(pool[i] for i in indices)
#             while 1:
#                 for i in reversed(range(r)):
#                     if indices[i] != n - 1:
#                         break
#                 else:
#                     return
#                 indices[i:] = [indices[i] + 1] * (r - i)
#                 yield tuple(pool[i] for i in indices)

#        def cwr2(iterable, r):
#            'Pure python version shown in the docs'
#            pool = tuple(iterable)
#            n = len(pool)
#            for indices in product(range(n), repeat=r):
#                if sorted(indices) == list(indices):
#                    yield tuple(pool[i] for i in indices)

        def numcombs(n, r):
            if not n:
                return 0 if r else 1
            return fact(n+r-1) / fact(r)/ fact(n-1)

        for n in range(7):
            values = [5*x-12 for x in range(n)]
            for r in range(n+2):
                result = list(cwr(values, r))

                self.assertEqual(len(result), numcombs(n, r))           # right number of combs
                self.assertEqual(len(result), len(set(result)))         # no repeats
                self.assertEqual(result, sorted(result))                # lexicographic order

                regular_combs = list(combinations(values, r))           # compare to combs without replacement
                if n == 0 or r <= 1:
                    self.assertEqual(result, regular_combs)            # cases that should be identical
                else:
                    self.assertTrue(set(result) >= set(regular_combs))     # rest should be supersets of regular combs

                for c in result:
                    self.assertEqual(len(c), r)                         # r-length combinations
                    noruns = [k for k,v in groupby(c)]                  # combo without consecutive repeats
                    self.assertEqual(len(noruns), len(set(noruns)))     # no repeats other than consecutive
                    self.assertEqual(list(c), sorted(c))                # keep original ordering
                    self.assertTrue(all(e in values for e in c))           # elements taken from input iterable
                    self.assertEqual(noruns,
                                     [e for e in values if e in c])     # comb is a subsequence of the input iterable
#                 self.assertEqual(result, list(cwr1(values, r)))         # matches first pure python version
#                 self.assertEqual(result, list(cwr2(values, r)))         # matches second pure python version

#                 for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#                     self.pickletest(proto, cwr(values,r))               # test pickling

#     @support.bigaddrspacetest
#     def test_combinations_with_replacement_overflow(self):
#         with self.assertRaises((OverflowError, MemoryError)):
#             combinations_with_replacement("AA", 2**30)

#         # Test implementation detail:  tuple re-use
#     @support.impl_detail("tuple reuse is specific to CPython")
#     def test_combinations_with_replacement_tuple_reuse(self):
#         cwr = combinations_with_replacement
#         self.assertEqual(len(set(map(id, cwr('abcde', 3)))), 1)
#         self.assertNotEqual(len(set(map(id, list(cwr('abcde', 3))))), 1)

    def test_permutations(self):
        self.assertRaises(TypeError, permutations)              # too few arguments
        self.assertRaises(TypeError, permutations, 'abc', 2, 1) # too many arguments
        self.assertRaises(TypeError, permutations, None)        # pool is not iterable
        self.assertRaises(ValueError, permutations, 'abc', -2)  # r is negative
        self.assertEqual(list(permutations('abc', 32)), [])     # r > n
        self.assertRaises(TypeError, permutations, 'abc', 's')  # r is not an int or None
        self.assertEqual(list(permutations(range(3), 2)),
                                           [(0,1), (0,2), (1,0), (1,2), (2,0), (2,1)])

#        def permutations1(iterable, r=None):
#             'Pure python version shown in the docs'
#             pool = tuple(iterable)
#             n = len(pool)
#             r = n if r is None else r
#             if r > n:
#                 return
#             indices = list(range(n))
#             cycles = list(range(n-r+1, n+1))[::-1]
#             yield tuple(pool[i] for i in indices[:r])
#             while n:
#                 for i in reversed(range(r)):
#                     cycles[i] -= 1
#                     if cycles[i] == 0:
#                         indices[i:] = indices[i+1:] + indices[i:i+1]
#                         cycles[i] = n - i
#                     else:
#                         j = cycles[i]
#                         indices[i], indices[-j] = indices[-j], indices[i]
#                         yield tuple(pool[i] for i in indices[:r])
#                         break
#                 else:
#                     return

#        def permutations2(iterable, r=None):
#            'Pure python version shown in the docs'
#            pool = tuple(iterable)
#            n = len(pool)
#            r = n if r is None else r
#            for indices in product(range(n), repeat=r):
#                if len(set(indices)) == r:
#                    yield tuple(pool[i] for i in indices)

        for n in range(7):
            values = [5*x-12 for x in range(n)]
            for r in range(n+2):
                result = list(permutations(values, r))
                self.assertEqual(len(result), 0 if r>n else fact(n) / fact(n-r))      # right number of perms
                self.assertEqual(len(result), len(set(result)))         # no repeats
                self.assertEqual(result, sorted(result))                # lexicographic order
                for p in result:
                    self.assertEqual(len(p), r)                         # r-length permutations
                    self.assertEqual(len(set(p)), r)                    # no duplicate elements
                    self.assertTrue(all(e in values for e in p))           # elements taken from input iterable
#                self.assertEqual(result, list(permutations1(values, r))) # matches first pure python version
#                self.assertEqual(result, list(permutations2(values, r))) # matches second pure python version
#                if r == n:
#                    self.assertEqual(result, list(permutations(values, None))) # test r as None
#                    self.assertEqual(result, list(permutations(values)))       # test default r

#                 for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#                     self.pickletest(proto, permutations(values, r))     # test pickling

#     @support.bigaddrspacetest
#     def test_permutations_overflow(self):
#         with self.assertRaises((OverflowError, MemoryError)):
#             permutations("A", 2**30)

#     @support.impl_detail("tuple reuse is specific to CPython")
#     def test_permutations_tuple_reuse(self):
#         self.assertEqual(len(set(map(id, permutations('abcde', 3)))), 1)
#         self.assertNotEqual(len(set(map(id, list(permutations('abcde', 3))))), 1)

    def test_combinatorics(self):
        # Test relationships between product(), permutations(),
        # combinations() and combinations_with_replacement().

        for n in range(5):
            s = 'ABCDEFG'[:n]
            for r in range(7):
                prod = list(product(s, repeat=r))
                cwr = list(combinations_with_replacement(s, r))
                perm = list(permutations(s, r))
                comb = list(combinations(s, r))

                # Check size
                self.assertEqual(len(prod), n**r)
                self.assertEqual(len(cwr), (fact(n+r-1) / fact(r)/ fact(n-1)) if n else (not r))
                self.assertEqual(len(perm), 0 if r>n else fact(n) / fact(n-r))
                self.assertEqual(len(comb), 0 if r>n else fact(n) / fact(r) / fact(n-r))

                # Check lexicographic order without repeated tuples
                self.assertEqual(prod, sorted(set(prod)))
                self.assertEqual(cwr, sorted(set(cwr)))
                self.assertEqual(perm, sorted(set(perm)))
                self.assertEqual(comb, sorted(set(comb)))

                # Check interrelationships
                self.assertEqual(cwr, [t for t in prod if sorted(t)==list(t)]) # cwr: prods which are sorted
                self.assertEqual(perm, [t for t in prod if len(set(t))==r])    # perm: prods with no dups
                self.assertEqual(comb, [t for t in perm if sorted(t)==list(t)]) # comb: perms that are sorted
                self.assertEqual(comb, [t for t in cwr if len(set(t))==r])      # comb: cwrs without dups
                # self.assertEqual(comb, list(filter(set(cwr).__contains__, perm)))     # comb: perm that is a cwr
                # self.assertEqual(comb, list(filter(set(perm).__contains__, cwr)))     # comb: cwr that is a perm
                self.assertEqual(comb, sorted(set(cwr) & set(perm)))            # comb: both a cwr and a perm

    def test_compress(self):
        self.assertEqual(list(compress(data='ABCDEF', selectors=[1,0,1,0,1,1])), list('ACEF'))
        self.assertEqual(list(compress('ABCDEF', [1,0,1,0,1,1])), list('ACEF'))
        self.assertEqual(list(compress('ABCDEF', [0,0,0,0,0,0])), list(''))
        self.assertEqual(list(compress('ABCDEF', [1,1,1,1,1,1])), list('ABCDEF'))
        self.assertEqual(list(compress('ABCDEF', [1,0,1])), list('AC'))
        self.assertEqual(list(compress('ABC', [0,1,1,1,1,1])), list('BC'))
        n = 10000
        data = chain.from_iterable(repeat(range(6), n))
        selectors = chain.from_iterable(repeat((0, 1)))
        self.assertEqual(list(compress(data, selectors)), [1,3,5] * n)
        self.assertRaises(TypeError, compress, None, range(6))      # 1st arg not iterable
        self.assertRaises(TypeError, compress, range(6), None)      # 2nd arg not iterable
        self.assertRaises(TypeError, compress, range(6))            # too few args
        self.assertRaises(TypeError, compress, range(6), None)      # too many args

#         # check copy, deepcopy, pickle
#         for op in [lambda a:copy.copy(a), lambda a:copy.deepcopy(a)] + picklecopiers:
#             for data, selectors, result1, result2 in [
#                 ('ABCDEF', [1,0,1,0,1,1], 'ACEF', 'CEF'),
#                 ('ABCDEF', [0,0,0,0,0,0], '', ''),
#                 ('ABCDEF', [1,1,1,1,1,1], 'ABCDEF', 'BCDEF'),
#                 ('ABCDEF', [1,0,1], 'AC', 'C'),
#                 ('ABC', [0,1,1,1,1,1], 'BC', 'C'),
#                 ]:

#                 self.assertEqual(list(op(compress(data=data, selectors=selectors))), list(result1))
#                 self.assertEqual(list(op(compress(data, selectors))), list(result1))
#                 testIntermediate = compress(data, selectors)
#                 if result1:
#                     next(testIntermediate)
#                     self.assertEqual(list(op(testIntermediate)), list(result2))


    def test_count(self):
        self.assertEqual(lzip('abc',count()), [('a', 0), ('b', 1), ('c', 2)])
        self.assertEqual(lzip('abc',count(3)), [('a', 3), ('b', 4), ('c', 5)])
        self.assertEqual(take(2, lzip('abc',count(3))), [('a', 3), ('b', 4)])
        self.assertEqual(take(2, zip('abc',count(-1))), [('a', -1), ('b', 0)])
        self.assertEqual(take(2, zip('abc',count(-3))), [('a', -3), ('b', -2)])
        self.assertRaises(TypeError, count, 2, 3, 4)
        self.assertRaises(TypeError, count, 'a')
        self.assertEqual(take(10, count(maxsize-5)),
                         list(range(maxsize-5, maxsize+5)))
        self.assertEqual(take(10, count(-maxsize-5)),
                         list(range(-maxsize-5, -maxsize+5)))
        self.assertEqual(take(3, count(3.25)), [3.25, 4.25, 5.25])
        self.assertEqual(take(3, count(3.25-4j)), [3.25-4j, 4.25-4j, 5.25-4j])
#         self.assertEqual(take(3, count(Decimal('1.1'))),
#                          [Decimal('1.1'), Decimal('2.1'), Decimal('3.1')])
#         self.assertEqual(take(3, count(Fraction(2, 3))),
#                          [Fraction(2, 3), Fraction(5, 3), Fraction(8, 3)])
        BIGINT = 1<<100
        self.assertEqual(take(3, count(BIGINT)), [BIGINT, BIGINT+1, BIGINT+2])
        c = count(3)
        self.assertEqual(repr(c), 'count(3)')
        next(c)
        self.assertEqual(repr(c), 'count(4)')
        c = count(-9)
        self.assertEqual(repr(c), 'count(-9)')
        next(c)
        self.assertEqual(next(c), -8)
        self.assertEqual(repr(count(10.25)), 'count(10.25)')
        self.assertEqual(repr(count(10.0)), 'count(10.0)')
        self.assertEqual(type(next(count(10.0))), float)
        for i in (maxsize-5, maxsize+5 ,-10, -1, 0, 10, maxsize-5, maxsize+5):
            # Test repr
            r1 = repr(count(i))
            r2 = ('count(%r)' % i)
            self.assertEqual(r1, r2)

#         # check copy, deepcopy, pickle
#         for value in -3, 3, maxsize-5, maxsize+5:
#             c = count(value)
#             self.assertEqual(next(copy.copy(c)), value)
#             self.assertEqual(next(copy.deepcopy(c)), value)
#             for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#                 self.pickletest(proto, count(value))

#         #check proper internal error handling for large "step' sizes
#         count(1, maxsize+5); sys.exc_info()

    def test_count_with_stride(self):
        self.assertEqual(lzip('abc',count(2,3)), [('a', 2), ('b', 5), ('c', 8)])
        self.assertEqual(lzip('abc',count(start=2,step=3)),
                         [('a', 2), ('b', 5), ('c', 8)])
        self.assertEqual(lzip('abc',count(step=-1)),
                         [('a', 0), ('b', -1), ('c', -2)])
        self.assertRaises(TypeError, count, 'a', 'b')
        self.assertEqual(lzip('abc',count(2,0)), [('a', 2), ('b', 2), ('c', 2)])
        self.assertEqual(lzip('abc',count(2,1)), [('a', 2), ('b', 3), ('c', 4)])
        self.assertEqual(lzip('abc',count(2,3)), [('a', 2), ('b', 5), ('c', 8)])
        self.assertEqual(take(20, count(maxsize-15, 3)), take(20, range(maxsize-15, maxsize+100, 3)))
        self.assertEqual(take(20, count(-maxsize-15, 3)), take(20, range(-maxsize-15,-maxsize+100, 3)))
        self.assertEqual(take(3, count(10, maxsize+5)),
                         list(range(10, 10+3*(maxsize+5), maxsize+5)))
        self.assertEqual(take(3, count(2, 1.25)), [2, 3.25, 4.5])
        self.assertEqual(take(3, count(2, 3.25-4j)), [2, 5.25-4j, 8.5-8j])
#         self.assertEqual(take(3, count(Decimal('1.1'), Decimal('.1'))),
#                          [Decimal('1.1'), Decimal('1.2'), Decimal('1.3')])
#         self.assertEqual(take(3, count(Fraction(2,3), Fraction(1,7))),
#                          [Fraction(2,3), Fraction(17,21), Fraction(20,21)])
        BIGINT = 1<<100
        self.assertEqual(take(3, count(step=BIGINT)), [0, BIGINT, 2*BIGINT])
        self.assertEqual(repr(take(3, count(10, 2.5))), repr([10, 12.5, 15.0]))
        c = count(3, 5)
        self.assertEqual(repr(c), 'count(3, 5)')
        next(c)
        self.assertEqual(repr(c), 'count(8, 5)')
        c = count(-9, 0)
        self.assertEqual(repr(c), 'count(-9, 0)')
        next(c)
        self.assertEqual(repr(c), 'count(-9, 0)')
        c = count(-9, -3)
        self.assertEqual(repr(c), 'count(-9, -3)')
        next(c)
        self.assertEqual(repr(c), 'count(-12, -3)')
        self.assertEqual(repr(c), 'count(-12, -3)')
        self.assertEqual(repr(count(10.5, 1.25)), 'count(10.5, 1.25)')
        self.assertEqual(repr(count(10.5, 1)), 'count(10.5)')           # suppress step=1 when it's an int
        self.assertEqual(repr(count(10.5, 1.00)), 'count(10.5, 1.0)')   # do show float values lilke 1.0
        self.assertEqual(repr(count(10, 1.00)), 'count(10, 1.0)')
        c = count(10, 1.0)
        self.assertEqual(type(next(c)), int)
        self.assertEqual(type(next(c)), float)
        for i in (maxsize-5, maxsize+5 ,-10, -1, 0, 10, maxsize-5, sys.maxsize+5):
            for j in  (maxsize-5, maxsize+5 ,-10, -1, 0, 1, 10, maxsize-5, maxsize+5):
                # Test repr
                r1 = repr(count(i, j))
                if j == 1:
                    r2 = ('count(%r)' % i)
                else:
                    r2 = ('count(%r, %r)' % (i, j))
                self.assertEqual(r1, r2)
#                 for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#                     self.pickletest(proto, count(i, j))

    def test_cycle(self):
        self.assertEqual(take(10, cycle('abc')), list('abcabcabca'))
        self.assertEqual(list(cycle('')), [])
        self.assertRaises(TypeError, cycle)
        self.assertRaises(TypeError, cycle, 5)
        self.assertEqual(list(islice(cycle(gen3()),10)), [0,1,2,0,1,2,0,1,2,0])

#         # check copy, deepcopy, pickle
#         c = cycle('abc')
#         self.assertEqual(next(c), 'a')
#         #simple copy currently not supported, because __reduce__ returns
#         #an internal iterator
#         #self.assertEqual(take(10, copy.copy(c)), list('bcabcabcab'))
#         self.assertEqual(take(10, copy.deepcopy(c)), list('bcabcabcab'))
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             self.assertEqual(take(10, pickle.loads(pickle.dumps(c, proto))),
#                              list('bcabcabcab'))
#             next(c)
#             self.assertEqual(take(10, pickle.loads(pickle.dumps(c, proto))),
#                              list('cabcabcabc'))
#             next(c)
#             next(c)
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             self.pickletest(proto, cycle('abc'))

#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             # test with partial consumed input iterable
#             it = iter('abcde')
#             c = cycle(it)
#             _ = [next(c) for i in range(2)]      # consume 2 of 5 inputs
#             p = pickle.dumps(c, proto)
#             d = pickle.loads(p)                  # rebuild the cycle object
#             self.assertEqual(take(20, d), list('cdeabcdeabcdeabcdeab'))

#             # test with completely consumed input iterable
#             it = iter('abcde')
#             c = cycle(it)
#             _ = [next(c) for i in range(7)]      # consume 7 of 5 inputs
#             p = pickle.dumps(c, proto)
#             d = pickle.loads(p)                  # rebuild the cycle object
#             self.assertEqual(take(20, d), list('cdeabcdeabcdeabcdeab'))

#     def test_cycle_setstate(self):
#         # Verify both modes for restoring state

#         # Mode 0 is efficient.  It uses an incompletely consumed input
#         # iterator to build a cycle object and then passes in state with
#         # a list of previously consumed values.  There is no data
#         # overlap between the two.
#         c = cycle('defg')
#         c.__setstate__((list('abc'), 0))
#         self.assertEqual(take(20, c), list('defgabcdefgabcdefgab'))

#         # Mode 1 is inefficient.  It starts with a cycle object built
#         # from an iterator over the remaining elements in a partial
#         # cycle and then passes in state with all of the previously
#         # seen values (this overlaps values included in the iterator).
#         c = cycle('defg')
#         c.__setstate__((list('abcdefg'), 1))
#         self.assertEqual(take(20, c), list('defgabcdefgabcdefgab'))

#         # The first argument to setstate needs to be a tuple
#         with self.assertRaises(TypeError):
#             cycle('defg').__setstate__([list('abcdefg'), 0])

#         # The first argument in the setstate tuple must be a list
#         with self.assertRaises(TypeError):
#             c = cycle('defg')
#             c.__setstate__((tuple('defg'), 0))
#         take(20, c)

#         # The second argument in the setstate tuple must be an int
#         with self.assertRaises(TypeError):
#             cycle('defg').__setstate__((list('abcdefg'), 'x'))

#         self.assertRaises(TypeError, cycle('').__setstate__, ())
#         self.assertRaises(TypeError, cycle('').__setstate__, ([],))

    def test_groupby(self):
        # Check whether it accepts arguments correctly
        self.assertEqual([], list(groupby([])))
        self.assertEqual([], list(groupby([], key=id)))
        self.assertRaises(TypeError, list, groupby('abc', []))
        self.assertRaises(TypeError, groupby, None)
        self.assertRaises(TypeError, groupby, 'abc', lambda x:x, 10)

        # Check normal input
        s = [(0, 10, 20), (0, 11,21), (0,12,21), (1,13,21), (1,14,22),
             (2,15,22), (3,16,23), (3,17,23)]
        dup = []
        for k, g in groupby(s, lambda r:r[0]):
            for elem in g:
                self.assertEqual(k, elem[0])
                dup.append(elem)
        self.assertEqual(s, dup)

#         # Check normal pickled
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             dup = []
#             for k, g in pickle.loads(pickle.dumps(groupby(s, testR), proto)):
#                 for elem in g:
#                     self.assertEqual(k, elem[0])
#                     dup.append(elem)
#             self.assertEqual(s, dup)

#         # Check nested case
        dup = []
        for k, g in groupby(s, testR):
            for ik, ig in groupby(g, testR2):
                for elem in ig:
                    self.assertEqual(k, elem[0])
                    self.assertEqual(ik, elem[2])
                    dup.append(elem)
        self.assertEqual(s, dup)

#         # Check nested and pickled
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             dup = []
#             for k, g in pickle.loads(pickle.dumps(groupby(s, testR), proto)):
#                 for ik, ig in pickle.loads(pickle.dumps(groupby(g, testR2), proto)):
#                     for elem in ig:
#                         self.assertEqual(k, elem[0])
#                         self.assertEqual(ik, elem[2])
#                         dup.append(elem)
#             self.assertEqual(s, dup)


#         # Check case where inner iterator is not used
        keys = [k for k, g in groupby(s, testR)]
        expectedkeys = set([r[0] for r in s])
        self.assertEqual(set(keys), expectedkeys)
        self.assertEqual(len(keys), len(expectedkeys))

#         # Check case where inner iterator is used after advancing the groupby
#         # iterator
        s = list(zip('AABBBAAAA', range(9)))
        it = groupby(s, testR)
        _, g1 = next(it)
        _, g2 = next(it)
        _, g3 = next(it)
        self.assertEqual(list(g1), [])
        self.assertEqual(list(g2), [])
        self.assertEqual(next(g3), ('A', 5))
        list(it)  # exhaust the groupby iterator
        self.assertEqual(list(g3), [])

#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             it = groupby(s, testR)
#             _, g = next(it)
#             next(it)
#             next(it)
#             self.assertEqual(list(pickle.loads(pickle.dumps(g, proto))), [])

        # Exercise pipes and filters style
        s = 'abracadabra'
        # sort s | uniq
        r = [k for k, g in groupby(sorted(s))]
        self.assertEqual(r, ['a', 'b', 'c', 'd', 'r'])
        # sort s | uniq -d
        r = [k for k, g in groupby(sorted(s)) if list(islice(g,1,2))]
        self.assertEqual(r, ['a', 'b', 'r'])
        # sort s | uniq -c
        r = [(len(list(g)), k) for k, g in groupby(sorted(s))]
        self.assertEqual(r, [(5, 'a'), (2, 'b'), (1, 'c'), (1, 'd'), (2, 'r')])
        # sort s | uniq -c | sort -rn | head -3
        r = sorted([(len(list(g)) , k) for k, g in groupby(sorted(s))], reverse=True)[:3]
        self.assertEqual(r, [(5, 'a'), (2, 'r'), (2, 'b')])

        # iter.__next__ failure
        class ExpectedError(Exception):
            pass
        def delayed_raise(n=0):
            for i in range(n):
                yield 'yo'
            raise ExpectedError
        def gulp(iterable, keyp=None, func=list):
            return [func(g) for k, g in groupby(iterable, keyp)]

        # iter.__next__ failure on outer object
        self.assertRaises(ExpectedError, gulp, delayed_raise(0))
        # iter.__next__ failure on inner object
        self.assertRaises(ExpectedError, gulp, delayed_raise(1))

        # __eq__ failure
        class DummyCmp:
            def __eq__(self, dst):
                raise ExpectedError
        s = [DummyCmp(), DummyCmp(), None]

        # __eq__ failure on outer object
        # self.assertRaises(ExpectedError, gulp, s, func=id)
        # __eq__ failure on inner object
        self.assertRaises(ExpectedError, gulp, s)

        # keyfunc failure
        def keyfunc(obj):
            if keyfunc.skip > 0:
                keyfunc.skip -= 1
                return obj
            else:
                raise ExpectedError

        # keyfunc failure on outer object
        keyfunc.skip = 0
        self.assertRaises(ExpectedError, gulp, [None], keyfunc)
        keyfunc.skip = 1
        self.assertRaises(ExpectedError, gulp, [None, None], keyfunc)

    def test_filter(self):
        self.assertEqual(list(filter(isEven, range(6))), [0,2,4])
        self.assertEqual(list(filter(None, [0,1,0,2,0])), [1,2])
        self.assertEqual(list(filter(bool, [0,1,0,2,0])), [1,2])
        self.assertEqual(take(4, filter(isEven, count())), [0,2,4,6])
        self.assertRaises(TypeError, filter)
        self.assertRaises(TypeError, filter, lambda x:x)
        self.assertRaises(TypeError, filter, lambda x:x, range(6), 7)
        self.assertRaises(TypeError, filter, isEven, 3)
        self.assertRaises(TypeError, next, filter(range(6), range(6)))

#         # check copy, deepcopy, pickle
#         ans = [0,2,4]

#         c = filter(isEven, range(6))
#         self.assertEqual(list(copy.copy(c)), ans)
#         c = filter(isEven, range(6))
#         self.assertEqual(list(copy.deepcopy(c)), ans)
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             c = filter(isEven, range(6))
#             self.assertEqual(list(pickle.loads(pickle.dumps(c, proto))), ans)
#             next(c)
#             self.assertEqual(list(pickle.loads(pickle.dumps(c, proto))), ans[1:])
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             c = filter(isEven, range(6))
#             self.pickletest(proto, c)

    def test_filterfalse(self):
        self.assertEqual(list(filterfalse(isEven, range(6))), [1,3,5])
        self.assertEqual(list(filterfalse(None, [0,1,0,2,0])), [0,0,0])
        self.assertEqual(list(filterfalse(bool, [0,1,0,2,0])), [0,0,0])
        self.assertEqual(take(4, filterfalse(isEven, count())), [1,3,5,7])
        self.assertRaises(TypeError, filterfalse)
        self.assertRaises(TypeError, filterfalse, lambda x:x)
        self.assertRaises(TypeError, filterfalse, lambda x:x, range(6), 7)
        self.assertRaises(TypeError, filterfalse, isEven, 3)
        self.assertRaises(TypeError, next, filterfalse(range(6), range(6)))
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             self.pickletest(proto, filterfalse(isEven, range(6)))

    def test_zip(self):
        # XXX This is rather silly now that builtin zip() calls zip()...
        ans = [(x,y) for x, y in zip('abc',count())]
        self.assertEqual(ans, [('a', 0), ('b', 1), ('c', 2)])
        self.assertEqual(list(zip('abc', range(6))), lzip('abc', range(6)))
        self.assertEqual(list(zip('abcdef', range(3))), lzip('abcdef', range(3)))
        self.assertEqual(take(3,zip('abcdef', count())), lzip('abcdef', range(3)))
        self.assertEqual(list(zip('abcdef')), lzip('abcdef'))
        self.assertEqual(list(zip()), lzip())
        self.assertRaises(TypeError, zip, 3)
        self.assertRaises(TypeError, zip, range(3), 3)
        self.assertEqual([tuple(list(pair)) for pair in zip('abc', 'def')],
                         lzip('abc', 'def'))
        self.assertEqual([pair for pair in zip('abc', 'def')],
                         lzip('abc', 'def'))

#     @support.impl_detail("tuple reuse is specific to CPython")
#     def test_zip_tuple_reuse(self):
#         ids = list(map(id, zip('abc', 'def')))
#         self.assertEqual(min(ids), max(ids))
#         ids = list(map(id, list(zip('abc', 'def'))))
#         self.assertEqual(len(dict.fromkeys(ids)), len(ids))

#         # check copy, deepcopy, pickle
#         ans = [(x,y) for x, y in copy.copy(zip('abc',count()))]
#         self.assertEqual(ans, [('a', 0), ('b', 1), ('c', 2)])

#         ans = [(x,y) for x, y in copy.deepcopy(zip('abc',count()))]
#         self.assertEqual(ans, [('a', 0), ('b', 1), ('c', 2)])

#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             ans = [(x,y) for x, y in pickle.loads(pickle.dumps(zip('abc',count()), proto))]
#             self.assertEqual(ans, [('a', 0), ('b', 1), ('c', 2)])

#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             testIntermediate = zip('abc',count())
#             next(testIntermediate)
#             ans = [(x,y) for x, y in pickle.loads(pickle.dumps(testIntermediate, proto))]
#             self.assertEqual(ans, [('b', 1), ('c', 2)])

#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             self.pickletest(proto, zip('abc', count()))

    def test_ziplongest(self):
        for args in [
                ['abc', range(6)],
                [range(6), 'abc'],
                [range(1000), range(2000,2100), range(3000,3050)],
                [range(1000), range(0), range(3000,3050), range(1200), range(1500)],
                [range(1000), range(0), range(3000,3050), range(1200), range(1500), range(0)],
            ]:
            target = [tuple([arg[i] if i < len(arg) else None for arg in args])
                      for i in range(max(map(len, args)))]
            self.assertEqual(list(zip_longest(*args)), target)
            self.assertEqual(list(zip_longest(*args, **{})), target)
            target = [tuple((e is None and 'X' or e) for e in t) for t in target]   # Replace None fills with 'X'
            self.assertEqual(list(zip_longest(*args, **dict(fillvalue='X'))), target)

        self.assertEqual(take(3,zip_longest('abcdef', count())), list(zip('abcdef', range(3)))) # take 3 from infinite input

        self.assertEqual(list(zip_longest()), list(zip()))
        self.assertEqual(list(zip_longest([])), list(zip([])))
        self.assertEqual(list(zip_longest('abcdef')), list(zip('abcdef')))

        self.assertEqual(list(zip_longest('abc', 'defg', **{})),
                         list(zip(list('abc')+[None], 'defg'))) # empty keyword dict
        self.assertRaises(TypeError, zip_longest, 3)
        self.assertRaises(TypeError, zip_longest, range(3), 3)

#         for stmt in [
#             "zip_longest('abc', fv=1)",
#             "zip_longest('abc', fillvalue=1, bogus_keyword=None)",
#         ]:
#             try:
#                 eval(stmt, globals(), locals())
#             except TypeError:
#                 pass
#             else:
#                 self.fail('Did not raise Type in:  ' + stmt)

        self.assertEqual([tuple(list(pair)) for pair in zip_longest('abc', 'def')],
                         list(zip('abc', 'def')))
        self.assertEqual([pair for pair in zip_longest('abc', 'def')],
                         list(zip('abc', 'def')))

#     @support.impl_detail("tuple reuse is specific to CPython")
#     def test_zip_longest_tuple_reuse(self):
#         ids = list(map(id, zip_longest('abc', 'def')))
#         self.assertEqual(min(ids), max(ids))
#         ids = list(map(id, list(zip_longest('abc', 'def'))))
#         self.assertEqual(len(dict.fromkeys(ids)), len(ids))

#     def test_zip_longest_pickling(self):
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             self.pickletest(proto, zip_longest("abc", "def"))
#             self.pickletest(proto, zip_longest("abc", "defgh"))
#             self.pickletest(proto, zip_longest("abc", "defgh", fillvalue=1))
#             self.pickletest(proto, zip_longest("", "defgh"))

    def test_bug_7244(self):

        class Repeater:
            # this class is similar to itertools.repeat
            def __init__(self, o, t, e):
                self.o = o
                self.t = int(t)
                self.e = e
            def __iter__(self): # its iterator is itself
                return self
            def __next__(self):
                if self.t > 0:
                    self.t -= 1
                    return self.o
                else:
                    raise self.e

        # Formerly this code in would fail in debug mode
        # with Undetected Error and Stop Iteration
        r1 = Repeater(1, 3, StopIteration)
        r2 = Repeater(2, 4, StopIteration)
        def run(r1, r2):
            result = []
            for i, j in zip_longest(r1, r2, fillvalue=0):
                # with support.captured_output('stdout'):
                #     print((i, j))
                result.append((i, j))
            return result
        self.assertEqual(run(r1, r2), [(1,2), (1,2), (1,2), (0,2)])

        # Formerly, the RuntimeError would be lost
        # and StopIteration would stop as expected
        r1 = Repeater(1, 3, RuntimeError)
        r2 = Repeater(2, 4, StopIteration)
        it = zip_longest(r1, r2, fillvalue=0)
        self.assertEqual(next(it), (1, 2))
        self.assertEqual(next(it), (1, 2))
        self.assertEqual(next(it), (1, 2))
        self.assertRaises(RuntimeError, next, it)

    def test_product(self):
        for args, result in [
            ([], [()]),                     # zero iterables
            (['ab'], [('a',), ('b',)]),     # one iterable
            ([range(2), range(3)], [(0,0), (0,1), (0,2), (1,0), (1,1), (1,2)]),     # two iterables
            ([range(0), range(2), range(3)], []),           # first iterable with zero length
            ([range(2), range(0), range(3)], []),           # middle iterable with zero length
            ([range(2), range(3), range(0)], []),           # last iterable with zero length
            ]:
            self.assertEqual(list(product(*args)), result)
            for r in range(4):
                self.assertEqual(list(product(*(args*r))),
                                 list(product(*args, **dict(repeat=r))))
        self.assertEqual(len(list(product(*[range(7)]*6))), 7**6)
        self.assertRaises(TypeError, product, range(6), None)

        # def product1(*args, **kwds):
        #     pools = list(map(tuple, args)) * kwds.get('repeat', 1)
        #     n = len(pools)
        #     if n == 0:
        #         yield ()
        #         return
        #     if any(len(pool) == 0 for pool in pools):
        #         return
        #     indices = [0] * n
        #     yield tuple(pool[i] for pool, i in zip(pools, indices))
        #     while 1:
        #         for i in reversed(range(n)):  # right to left
        #             if indices[i] == len(pools[i]) - 1:
        #                 continue
        #             indices[i] += 1
        #             for j in range(i+1, n):
        #                 indices[j] = 0
        #             yield tuple(pool[i] for pool, i in zip(pools, indices))
        #             break
        #         else:
        #             return

        # def product2(*args, **kwds):
        #     'Pure python version used in docs'
        #     pools = list(map(tuple, args)) * kwds.get('repeat', 1)
        #     result = [[]]
        #     for pool in pools:
        #         result = [x+[y] for x in result for y in pool]
        #     for prod in result:
        #         yield tuple(prod)

        # argtypes = ['', 'abc', '', range(0), range(4), dict(a=1, b=2, c=3),
        #             set('abcdefg'), range(11), tuple(range(13))]
        # for i in range(100):
        #     args = [random.choice(argtypes) for j in range(random.randrange(5))]
        #     expected_len = prod(map(len, args))
        #     self.assertEqual(len(list(product(*args))), expected_len)
        #     self.assertEqual(list(product(*args)), list(product1(*args)))
        #     self.assertEqual(list(product(*args)), list(product2(*args)))
        #     args = map(iter, args)
        #     self.assertEqual(len(list(product(*args))), expected_len)

#     @support.bigaddrspacetest
#     def test_product_overflow(self):
#         with self.assertRaises((OverflowError, MemoryError)):
#             product(*(['ab']*2**5), repeat=2**25)

#     @support.impl_detail("tuple reuse is specific to CPython")
#     def test_product_tuple_reuse(self):
#         self.assertEqual(len(set(map(id, product('abc', 'def')))), 1)
#         self.assertNotEqual(len(set(map(id, list(product('abc', 'def'))))), 1)

#     def test_product_pickling(self):
#         # check copy, deepcopy, pickle
#         for args, result in [
#             ([], [()]),                     # zero iterables
#             (['ab'], [('a',), ('b',)]),     # one iterable
#             ([range(2), range(3)], [(0,0), (0,1), (0,2), (1,0), (1,1), (1,2)]),     # two iterables
#             ([range(0), range(2), range(3)], []),           # first iterable with zero length
#             ([range(2), range(0), range(3)], []),           # middle iterable with zero length
#             ([range(2), range(3), range(0)], []),           # last iterable with zero length
#             ]:
#             self.assertEqual(list(copy.copy(product(*args))), result)
#             self.assertEqual(list(copy.deepcopy(product(*args))), result)
#             for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#                 self.pickletest(proto, product(*args))

#     def test_product_issue_25021(self):
#         # test that indices are properly clamped to the length of the tuples
#         p = product((1, 2),(3,))
#         p.__setstate__((0, 0x1000))  # will access tuple element 1 if not clamped
#         self.assertEqual(next(p), (2, 3))
#         # test that empty tuple in the list will result in an immediate StopIteration
#         p = product((1, 2), (), (3,))
#         p.__setstate__((0, 0, 0x1000))  # will access tuple element 1 if not clamped
#         self.assertRaises(StopIteration, next, p)

    def test_repeat(self):
        self.assertEqual(list(repeat(object='a', times=3)), ['a', 'a', 'a'])
#         self.assertEqual(lzip(range(3),repeat('a')),
#                          [(0, 'a'), (1, 'a'), (2, 'a')])
        self.assertEqual(list(repeat('a', 3)), ['a', 'a', 'a'])
        self.assertEqual(take(3, repeat('a')), ['a', 'a', 'a'])
        self.assertEqual(list(repeat('a', 0)), [])
        self.assertEqual(list(repeat('a', -3)), [])
        self.assertRaises(TypeError, repeat)
        self.assertRaises(TypeError, repeat, None, 3, 4)
        self.assertRaises(TypeError, repeat, None, 'a')
        r = repeat(1+0j)
        self.assertEqual(repr(r), 'repeat((1+0j))')
        r = repeat(1+0j, 5)
        self.assertEqual(repr(r), 'repeat((1+0j), 5)')
        list(r)
        self.assertEqual(repr(r), 'repeat((1+0j), 0)')

#         # check copy, deepcopy, pickle
#         c = repeat(object='a', times=10)
#         self.assertEqual(next(c), 'a')
#         self.assertEqual(take(2, copy.copy(c)), list('a' * 2))
#         self.assertEqual(take(2, copy.deepcopy(c)), list('a' * 2))
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             self.pickletest(proto, repeat(object='a', times=10))

    def test_repeat_with_negative_times(self):
        self.assertEqual(repr(repeat('a', -1)), "repeat('a', 0)")
        self.assertEqual(repr(repeat('a', -2)), "repeat('a', 0)")
        self.assertEqual(repr(repeat('a', times=-1)), "repeat('a', 0)")
        self.assertEqual(repr(repeat('a', times=-2)), "repeat('a', 0)")

    def test_map(self):
        self.assertEqual(list(map(operator.pow, range(3), range(1,7))),
                         [0**1, 1**2, 2**3])
        self.assertEqual(list(map(tupleize, 'abc', range(5))),
                         [('a',0),('b',1),('c',2)])
        self.assertEqual(list(map(tupleize, 'abc', count())),
                         [('a',0),('b',1),('c',2)])
        self.assertEqual(take(2,map(tupleize, 'abc', count())),
                         [('a',0),('b',1)])
        self.assertEqual(list(map(operator.pow, [])), [])
        self.assertRaises(TypeError, map)
        # self.assertRaises(TypeError, list, map(None, range(3), range(3)))
        self.assertRaises(TypeError, map, operator.neg)
        self.assertRaises(TypeError, next, map(10, range(5)))
        self.assertRaises(ValueError, next, map(errfunc, [4], [5]))
        self.assertRaises(TypeError, next, map(onearg, [4], [5]))

#         # check copy, deepcopy, pickle
#         ans = [('a',0),('b',1),('c',2)]

#         c = map(tupleize, 'abc', count())
#         self.assertEqual(list(copy.copy(c)), ans)

#         c = map(tupleize, 'abc', count())
#         self.assertEqual(list(copy.deepcopy(c)), ans)

#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             c = map(tupleize, 'abc', count())
#             self.pickletest(proto, c)

    def test_starmap(self):
        self.assertEqual(list(starmap(operator.pow, zip(range(3), range(1,7)))),
                         [0**1, 1**2, 2**3])
        self.assertEqual(take(3, starmap(operator.pow, zip(count(), count(1)))),
                         [0**1, 1**2, 2**3])
        self.assertEqual(list(starmap(operator.pow, [])), [])
        self.assertEqual(list(starmap(operator.pow, [iter([4,5])])), [4**5])
        self.assertRaises(TypeError, list, starmap(operator.pow, [None]))
        self.assertRaises(TypeError, starmap)
        self.assertRaises(TypeError, starmap, operator.pow, [(4,5)], 'extra')
        self.assertRaises(TypeError, next, starmap(10, [(4,5)]))
        self.assertRaises(ValueError, next, starmap(errfunc, [(4,5)]))
        self.assertRaises(TypeError, next, starmap(onearg, [(4,5)]))

#         # check copy, deepcopy, pickle
#         ans = [0**1, 1**2, 2**3]

#         c = starmap(operator.pow, zip(range(3), range(1,7)))
#         self.assertEqual(list(copy.copy(c)), ans)

#         c = starmap(operator.pow, zip(range(3), range(1,7)))
#         self.assertEqual(list(copy.deepcopy(c)), ans)

#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             c = starmap(operator.pow, zip(range(3), range(1,7)))
#             self.pickletest(proto, c)

    def test_islice(self):
        for args in [          # islice(args) should agree with range(args)
                (10, 20, 3),
                (10, 3, 20),
                (10, 20),
                (10, 10),
                (10, 3),
                (20,)
                ]:
            self.assertEqual(list(islice(range(100), *args)),
                             list(range(*args)))

        for args, tgtargs in [  # Stop when seqn is exhausted
                ((10, 110, 3), ((10, 100, 3))),
                ((10, 110), ((10, 100))),
                ((110,), (100,))
                ]:
            self.assertEqual(list(islice(range(100), *args)),
                             list(range(*tgtargs)))

        # Test stop=None
        self.assertEqual(list(islice(range(10), None)), list(range(10)))
        self.assertEqual(list(islice(range(10), None, None)), list(range(10)))
        self.assertEqual(list(islice(range(10), None, None, None)), list(range(10)))
        self.assertEqual(list(islice(range(10), 2, None)), list(range(2, 10)))
        self.assertEqual(list(islice(range(10), 1, None, 2)), list(range(1, 10, 2)))

        # Test number of items consumed     SF #1171417
        it = iter(range(10))
        self.assertEqual(list(islice(it, 3)), list(range(3)))
        self.assertEqual(list(it), list(range(3, 10)))

        it = iter(range(10))
        self.assertEqual(list(islice(it, 3, 3)), [])
        self.assertEqual(list(it), list(range(3, 10)))

        # # Test invalid arguments
        ra = range(10)
        self.assertRaises(TypeError, islice, ra)
        self.assertRaises(TypeError, islice, ra, 1, 2, 3, 4)
        self.assertRaises(ValueError, islice, ra, -5, 10, 1)
        self.assertRaises(ValueError, islice, ra, 1, -5, -1)
        self.assertRaises(ValueError, islice, ra, 1, 10, -1)
        self.assertRaises(ValueError, islice, ra, 1, 10, 0)
        self.assertRaises(ValueError, islice, ra, 'a')
        self.assertRaises(ValueError, islice, ra, 'a', 1)
        self.assertRaises(ValueError, islice, ra, 1, 'a')
        self.assertRaises(ValueError, islice, ra, 'a', 1, 1)
        self.assertRaises(ValueError, islice, ra, 1, 'a', 1)
        self.assertEqual(len(list(islice(count(), 1, 10, maxsize))), 1)

        # Issue #10323:  Less islice in a predictable state
        c = count()
        self.assertEqual(list(islice(c, 1, 3, 50)), [1])
        self.assertEqual(next(c), 3)

#         # check copy, deepcopy, pickle
#         for args in [          # islice(args) should agree with range(args)
#                 (10, 20, 3),
#                 (10, 3, 20),
#                 (10, 20),
#                 (10, 3),
#                 (20,)
#                 ]:
#             self.assertEqual(list(copy.copy(islice(range(100), *args))),
#                              list(range(*args)))
#             self.assertEqual(list(copy.deepcopy(islice(range(100), *args))),
#                              list(range(*args)))
#             for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#                 self.pickletest(proto, islice(range(100), *args))

#         # Issue #21321: check source iterator is not referenced
#         # from islice() after the latter has been exhausted
#         it = (x for x in (1, 2))
#         wr = weakref.ref(it)
#         it = islice(it, 1)
#         self.assertIsNotNone(wr())
#         list(it) # exhaust the iterator
#         support.gc_collect()
#         self.assertIsNone(wr())

        # Issue #30537: islice can accept integer-like objects as
        # arguments
        class IntLike(object):
            def __init__(self, val):
                self.val = val
            def __index__(self):
                return self.val
        self.assertEqual(list(islice(range(100), IntLike(10))), list(range(10)))
        self.assertEqual(list(islice(range(100), IntLike(10), IntLike(50))),
                         list(range(10, 50)))
        self.assertEqual(list(islice(range(100), IntLike(10), IntLike(50), IntLike(5))),
                         list(range(10,50,5)))

    def test_takewhile(self):
        data = [1, 3, 5, 20, 2, 4, 6, 8]
        self.assertEqual(list(takewhile(underten, data)), [1, 3, 5])
        self.assertEqual(list(takewhile(underten, [])), [])
        self.assertRaises(TypeError, takewhile)
        self.assertRaises(TypeError, takewhile, operator.pow)
        self.assertRaises(TypeError, takewhile, operator.pow, [(4,5)], 'extra')
        self.assertRaises(TypeError, next, takewhile(10, [(4,5)]))
        self.assertRaises(ValueError, next, takewhile(errfunc, [(4,5)]))
        t = takewhile(bool, [1, 1, 1, 0, 0, 0])
        self.assertEqual(list(t), [1, 1, 1])
        self.assertRaises(StopIteration, next, t)

#         # check copy, deepcopy, pickle
#         self.assertEqual(list(copy.copy(takewhile(underten, data))), [1, 3, 5])
#         self.assertEqual(list(copy.deepcopy(takewhile(underten, data))),
#                         [1, 3, 5])
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             self.pickletest(proto, takewhile(underten, data))

    def test_dropwhile(self):
        data = [1, 3, 5, 20, 2, 4, 6, 8]
        self.assertEqual(list(dropwhile(underten, data)), [20, 2, 4, 6, 8])
        self.assertEqual(list(dropwhile(underten, [])), [])
        self.assertRaises(TypeError, dropwhile)
        self.assertRaises(TypeError, dropwhile, operator.pow)
        self.assertRaises(TypeError, dropwhile, operator.pow, [(4,5)], 'extra')
        self.assertRaises(TypeError, next, dropwhile(10, [(4,5)]))
        self.assertRaises(ValueError, next, dropwhile(errfunc, [(4,5)]))

#         # check copy, deepcopy, pickle
#         self.assertEqual(list(copy.copy(dropwhile(underten, data))), [20, 2, 4, 6, 8])
#         self.assertEqual(list(copy.deepcopy(dropwhile(underten, data))),
#                         [20, 2, 4, 6, 8])
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             self.pickletest(proto, dropwhile(underten, data))

#     def test_tee(self):
#         n = 200

#         a, b = tee([])        # test empty iterator
#         self.assertEqual(list(a), [])
#         self.assertEqual(list(b), [])

#         a, b = tee(irange(n)) # test 100% interleaved
#         self.assertEqual(lzip(a,b), lzip(range(n), range(n)))

#         a, b = tee(irange(n)) # test 0% interleaved
#         self.assertEqual(list(a), list(range(n)))
#         self.assertEqual(list(b), list(range(n)))

#         a, b = tee(irange(n)) # test dealloc of leading iterator
#         for i in range(100):
#             self.assertEqual(next(a), i)
#         del a
#         self.assertEqual(list(b), list(range(n)))

#         a, b = tee(irange(n)) # test dealloc of trailing iterator
#         for i in range(100):
#             self.assertEqual(next(a), i)
#         del b
#         self.assertEqual(list(a), list(range(100, n)))

#         for j in range(5):   # test randomly interleaved
#             order = [0]*n + [1]*n
#             random.shuffle(order)
#             lists = ([], [])
#             its = tee(irange(n))
#             for i in order:
#                 value = next(its[i])
#                 lists[i].append(value)
#             self.assertEqual(lists[0], list(range(n)))
#             self.assertEqual(lists[1], list(range(n)))

#         # test argument format checking
#         self.assertRaises(TypeError, tee)
#         self.assertRaises(TypeError, tee, 3)
#         self.assertRaises(TypeError, tee, [1,2], 'x')
#         self.assertRaises(TypeError, tee, [1,2], 3, 'x')

#         # tee object should be instantiable
#         a, b = tee('abc')
#         c = type(a)('def')
#         self.assertEqual(list(c), list('def'))

#         # test long-lagged and multi-way split
#         a, b, c = tee(range(2000), 3)
#         for i in range(100):
#             self.assertEqual(next(a), i)
#         self.assertEqual(list(b), list(range(2000)))
#         self.assertEqual([next(c), next(c)], list(range(2)))
#         self.assertEqual(list(a), list(range(100,2000)))
#         self.assertEqual(list(c), list(range(2,2000)))

#         # test values of n
#         self.assertRaises(TypeError, tee, 'abc', 'invalid')
#         self.assertRaises(ValueError, tee, [], -1)
#         for n in range(5):
#             result = tee('abc', n)
#             self.assertEqual(type(result), tuple)
#             self.assertEqual(len(result), n)
#             self.assertEqual([list(x) for x in result], [list('abc')]*n)

#         # tee pass-through to copyable iterator
#         a, b = tee('abc')
#         c, d = tee(a)
#         self.assertTrue(a is c)

#         # test tee_new
#         t1, t2 = tee('abc')
#         tnew = type(t1)
#         self.assertRaises(TypeError, tnew)
#         self.assertRaises(TypeError, tnew, 10)
#         t3 = tnew(t1)
#         self.assertTrue(list(t1) == list(t2) == list(t3) == list('abc'))

#         # test that tee objects are weak referencable
#         a, b = tee(range(10))
#         p = weakref.proxy(a)
#         self.assertEqual(getattr(p, '__class__'), type(b))
#         del a
#         self.assertRaises(ReferenceError, getattr, p, '__class__')

#         ans = list('abc')
#         long_ans = list(range(10000))

#         # check copy
#         a, b = tee('abc')
#         self.assertEqual(list(copy.copy(a)), ans)
#         self.assertEqual(list(copy.copy(b)), ans)
#         a, b = tee(list(range(10000)))
#         self.assertEqual(list(copy.copy(a)), long_ans)
#         self.assertEqual(list(copy.copy(b)), long_ans)

#         # check partially consumed copy
#         a, b = tee('abc')
#         take(2, a)
#         take(1, b)
#         self.assertEqual(list(copy.copy(a)), ans[2:])
#         self.assertEqual(list(copy.copy(b)), ans[1:])
#         self.assertEqual(list(a), ans[2:])
#         self.assertEqual(list(b), ans[1:])
#         a, b = tee(range(10000))
#         take(100, a)
#         take(60, b)
#         self.assertEqual(list(copy.copy(a)), long_ans[100:])
#         self.assertEqual(list(copy.copy(b)), long_ans[60:])
#         self.assertEqual(list(a), long_ans[100:])
#         self.assertEqual(list(b), long_ans[60:])

#         # check deepcopy
#         a, b = tee('abc')
#         self.assertEqual(list(copy.deepcopy(a)), ans)
#         self.assertEqual(list(copy.deepcopy(b)), ans)
#         self.assertEqual(list(a), ans)
#         self.assertEqual(list(b), ans)
#         a, b = tee(range(10000))
#         self.assertEqual(list(copy.deepcopy(a)), long_ans)
#         self.assertEqual(list(copy.deepcopy(b)), long_ans)
#         self.assertEqual(list(a), long_ans)
#         self.assertEqual(list(b), long_ans)

#         # check partially consumed deepcopy
#         a, b = tee('abc')
#         take(2, a)
#         take(1, b)
#         self.assertEqual(list(copy.deepcopy(a)), ans[2:])
#         self.assertEqual(list(copy.deepcopy(b)), ans[1:])
#         self.assertEqual(list(a), ans[2:])
#         self.assertEqual(list(b), ans[1:])
#         a, b = tee(range(10000))
#         take(100, a)
#         take(60, b)
#         self.assertEqual(list(copy.deepcopy(a)), long_ans[100:])
#         self.assertEqual(list(copy.deepcopy(b)), long_ans[60:])
#         self.assertEqual(list(a), long_ans[100:])
#         self.assertEqual(list(b), long_ans[60:])

#         # check pickle
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             self.pickletest(proto, iter(tee('abc')))
#             a, b = tee('abc')
#             self.pickletest(proto, a, compare=ans)
#             self.pickletest(proto, b, compare=ans)

#     # Issue 13454: Crash when deleting backward iterator from tee()
#     def test_tee_del_backward(self):
#         forward, backward = tee(repeat(None, 20000000))
#         try:
#             any(forward)  # exhaust the iterator
#             del backward
#         except:
#             del forward, backward
#             raise

#     def test_tee_reenter(self):
#         class I:
#             first = True
#             def __iter__(self):
#                 return self
#             def __next__(self):
#                 first = self.first
#                 self.first = False
#                 if first:
#                     return next(b)

#         a, b = tee(I())
#         with self.assertRaisesRegex(RuntimeError, "tee"):
#             next(a)

#     def test_tee_concurrent(self):
#         start = threading.Event()
#         finish = threading.Event()
#         class I:
#             def __iter__(self):
#                 return self
#             def __next__(self):
#                 start.set()
#                 finish.wait()

#         a, b = tee(I())
#         thread = threading.Thread(target=next, args=[a])
#         thread.start()
#         try:
#             start.wait()
#             with self.assertRaisesRegex(RuntimeError, "tee"):
#                 next(b)
#         finally:
#             finish.set()
#             thread.join()

    def test_StopIteration(self):
        self.assertRaises(StopIteration, next, zip())

        for f in (chain, cycle, zip, groupby):
            self.assertRaises(StopIteration, next, f([]))
            self.assertRaises(StopIteration, next, f(StopNow()))

        self.assertRaises(StopIteration, next, islice([], None))
        self.assertRaises(StopIteration, next, islice(StopNow(), None))

#         p, q = tee([])
#         self.assertRaises(StopIteration, next, p)
#         self.assertRaises(StopIteration, next, q)
#         p, q = tee(StopNow())
#         self.assertRaises(StopIteration, next, p)
#         self.assertRaises(StopIteration, next, q)

        self.assertRaises(StopIteration, next, repeat(None, 0))

        for f in (filter, filterfalse, map, takewhile, dropwhile, starmap):
            self.assertRaises(StopIteration, next, f(lambda x:x, []))
            self.assertRaises(StopIteration, next, f(lambda x:x, StopNow()))

class TestExamples(unittest.TestCase):

    def test_accumulate(self):
        self.assertEqual(list(accumulate([1,2,3,4,5])), [1, 3, 6, 10, 15])

#     def test_accumulate_reducible(self):
#         # check copy, deepcopy, pickle
#         data = [1, 2, 3, 4, 5]
#         accumulated = [1, 3, 6, 10, 15]

#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             it = accumulate(data)
#             self.assertEqual(list(pickle.loads(pickle.dumps(it, proto))), accumulated[:])
#             self.assertEqual(next(it), 1)
#             self.assertEqual(list(pickle.loads(pickle.dumps(it, proto))), accumulated[1:])
#         it = accumulate(data)
#         self.assertEqual(next(it), 1)
#         self.assertEqual(list(copy.deepcopy(it)), accumulated[1:])
#         self.assertEqual(list(copy.copy(it)), accumulated[1:])

    def test_accumulate_reducible_none(self):
        # Issue #25718: total is None
        it = accumulate([None, None, None], operator.is_)
        self.assertEqual(next(it), None)
#         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
#             it_copy = pickle.loads(pickle.dumps(it, proto))
#             self.assertEqual(list(it_copy), [True, False])
#         self.assertEqual(list(copy.deepcopy(it)), [True, False])
#         self.assertEqual(list(copy.copy(it)), [True, False])

    def test_chain(self):
        self.assertEqual(''.join(chain('ABC', 'DEF')), 'ABCDEF')

    def test_chain_from_iterable(self):
        self.assertEqual(''.join(chain.from_iterable(['ABC', 'DEF'])), 'ABCDEF')

    def test_combinations(self):
        self.assertEqual(list(combinations('ABCD', 2)),
                         [('A','B'), ('A','C'), ('A','D'), ('B','C'), ('B','D'), ('C','D')])
        self.assertEqual(list(combinations(range(4), 3)),
                         [(0,1,2), (0,1,3), (0,2,3), (1,2,3)])

    def test_combinations_with_replacement(self):
        self.assertEqual(list(combinations_with_replacement('ABC', 2)),
                         [('A','A'), ('A','B'), ('A','C'), ('B','B'), ('B','C'), ('C','C')])

    def test_compress(self):
        self.assertEqual(list(compress('ABCDEF', [1,0,1,0,1,1])), list('ACEF'))

    def test_count(self):
        self.assertEqual(list(islice(count(10), 5)), [10, 11, 12, 13, 14])

    def test_cycle(self):
        self.assertEqual(list(islice(cycle('ABCD'), 12)), list('ABCDABCDABCD'))

    def test_dropwhile(self):
        self.assertEqual(list(dropwhile(lambda x: x<5, [1,4,6,4,1])), [6,4,1])

    def test_groupby(self):
        self.assertEqual([k for k, g in groupby('AAAABBBCCDAABBB')],
                         list('ABCDAB'))
        self.assertEqual([(list(g)) for k, g in groupby('AAAABBBCCD')],
                         [list('AAAA'), list('BBB'), list('CC'), list('D')])

#     def test_filter(self):
#         self.assertEqual(list(filter(lambda x: x%2, range(10))), [1,3,5,7,9])

    def test_filterfalse(self):
        self.assertEqual(list(filterfalse(lambda x: x%2, range(10))), [0,2,4,6,8])

    def test_map(self):
        self.assertEqual(list(map(pow, (2,3,10), (5,2,3))), [32, 9, 1000])

    def test_islice(self):
        self.assertEqual(list(islice('ABCDEFG', 2)), list('AB'))
        self.assertEqual(list(islice('ABCDEFG', 2, 4)), list('CD'))
        self.assertEqual(list(islice('ABCDEFG', 2, None)), list('CDEFG'))
        self.assertEqual(list(islice('ABCDEFG', 0, None, 2)), list('ACEG'))

    def test_zip(self):
        self.assertEqual(list(zip('ABCD', 'xy')), [('A', 'x'), ('B', 'y')])

    def test_zip_longest(self):
        self.assertEqual(list(zip_longest('ABCD', 'xy', fillvalue='-')),
                         [('A', 'x'), ('B', 'y'), ('C', '-'), ('D', '-')])

    def test_permutations(self):
        self.assertEqual(list(permutations('ABCD', 2)),
                         list(map(tuple, 'AB AC AD BA BC BD CA CB CD DA DB DC'.split())))
        self.assertEqual(list(permutations(range(3))),
                         [(0,1,2), (0,2,1), (1,0,2), (1,2,0), (2,0,1), (2,1,0)])

    def test_product(self):
        self.assertEqual(list(product('ABCD', 'xy')),
                         list(map(tuple, 'Ax Ay Bx By Cx Cy Dx Dy'.split())))
        self.assertEqual(list(product(range(2), repeat=3)),
                        [(0,0,0), (0,0,1), (0,1,0), (0,1,1),
                         (1,0,0), (1,0,1), (1,1,0), (1,1,1)])

    def test_repeat(self):
        self.assertEqual(list(repeat(10, 3)), [10, 10, 10])

    def test_stapmap(self):
        self.assertEqual(list(starmap(pow, [(2,5), (3,2), (10,3)])),
                         [32, 9, 1000])

    def test_takewhile(self):
        self.assertEqual(list(takewhile(lambda x: x<5, [1,4,6,4,1])), [1,4])


# class TestPurePythonRoughEquivalents(unittest.TestCase):

#     @staticmethod
#     def islice(iterable, *args):
#         s = slice(*args)
#         start, stop, step = s.start or 0, s.stop or sys.maxsize, s.step or 1
#         it = iter(range(start, stop, step))
#         try:
#             nexti = next(it)
#         except StopIteration:
#             # Consume *iterable* up to the *start* position.
#             for i, element in zip(range(start), iterable):
#                 pass
#             return
#         try:
#             for i, element in enumerate(iterable):
#                 if i == nexti:
#                     yield element
#                     nexti = next(it)
#         except StopIteration:
#             # Consume to *stop*.
#             for i, element in zip(range(i + 1, stop), iterable):
#                 pass

#     def test_islice_recipe(self):
#         self.assertEqual(list(self.islice('ABCDEFG', 2)), list('AB'))
#         self.assertEqual(list(self.islice('ABCDEFG', 2, 4)), list('CD'))
#         self.assertEqual(list(self.islice('ABCDEFG', 2, None)), list('CDEFG'))
#         self.assertEqual(list(self.islice('ABCDEFG', 0, None, 2)), list('ACEG'))
#         # Test items consumed.
#         it = iter(range(10))
#         self.assertEqual(list(self.islice(it, 3)), list(range(3)))
#         self.assertEqual(list(it), list(range(3, 10)))
#         it = iter(range(10))
#         self.assertEqual(list(self.islice(it, 3, 3)), [])
#         self.assertEqual(list(it), list(range(3, 10)))
#         # Test that slice finishes in predictable state.
#         c = count()
#         self.assertEqual(list(self.islice(c, 1, 3, 50)), [1])
#         self.assertEqual(next(c), 3)


class TestGC(unittest.TestCase):

    def makecycle(self, iterator, container):
        container.append(iterator)
        next(iterator)
        del container, iterator

    def test_accumulate(self):
        a = []
        self.makecycle(accumulate([1,2,a,3]), a)

    def test_chain(self):
        a = []
        self.makecycle(chain(a), a)

    def test_chain_from_iterable(self):
        a = []
        self.makecycle(chain.from_iterable([a]), a)

    def test_combinations(self):
        a = []
        self.makecycle(combinations([1,2,a,3], 3), a)

    def test_combinations_with_replacement(self):
        a = []
        self.makecycle(combinations_with_replacement([1,2,a,3], 3), a)

    def test_compress(self):
        a = []
        self.makecycle(compress('ABCDEF', [1,0,1,0,1,0]), a)

    def test_count(self):
        a = []
        Int = type('Int', (int,), dict(x=a))
        self.makecycle(count(Int(0), Int(1)), a)

    def test_cycle(self):
        a = []
        self.makecycle(cycle([a]*2), a)

    def test_dropwhile(self):
        a = []
        self.makecycle(dropwhile(bool, [0, a, a]), a)

    def test_groupby(self):
        a = []
        self.makecycle(groupby([a]*2, lambda x:x), a)

#    def test_issue2246(self):
#        # Issue 2246 -- the _grouper iterator was not included in GC
#        n = 10
#        keyfunc = lambda x: x
#        for i, j in groupby(range(n), key=keyfunc):
#            keyfunc.__dict__.setdefault('x',[]).append(j)

    def test_filter(self):
        a = []
        self.makecycle(filter(lambda x:True, [a]*2), a)

    def test_filterfalse(self):
        a = []
        self.makecycle(filterfalse(lambda x:False, a), a)

    def test_zip(self):
        a = []
        self.makecycle(zip([a]*2, [a]*3), a)

    def test_zip_longest(self):
        a = []
        self.makecycle(zip_longest([a]*2, [a]*3), a)
        b = [a, None]
        self.makecycle(zip_longest([a]*2, [a]*3, fillvalue=b), a)

    def test_map(self):
        a = []
        self.makecycle(map(lambda x:x, [a]*2), a)

    def test_islice(self):
        a = []
        self.makecycle(islice([a]*2, None), a)

    def test_permutations(self):
        a = []
        self.makecycle(permutations([1,2,a,3], 3), a)

    def test_product(self):
        a = []
        self.makecycle(product([1,2,a,3], repeat=3), a)

    def test_repeat(self):
        a = []
        self.makecycle(repeat(a), a)

    def test_starmap(self):
        a = []
        self.makecycle(starmap(lambda *t: t, [(a,a)]*2), a)

    def test_takewhile(self):
        a = []
        self.makecycle(takewhile(bool, [1, 0, a, a]), a)

def R(seqn):
    'Regular generator'
    for i in seqn:
        yield i

class G:
    'Sequence using __getitem__'
    def __init__(self, seqn):
        self.seqn = seqn
    def __getitem__(self, i):
        return self.seqn[i]

class I:
    'Sequence using iterator protocol'
    def __init__(self, seqn):
        self.seqn = seqn
        self.i = 0
    def __iter__(self):
        return self
    def __next__(self):
        if self.i >= len(self.seqn): raise StopIteration
        v = self.seqn[self.i]
        self.i += 1
        return v

class Ig:
    'Sequence using iterator protocol defined with a generator'
    def __init__(self, seqn):
        self.seqn = seqn
        self.i = 0
    def __iter__(self):
        for val in self.seqn:
            yield val

class X:
    'Missing __getitem__ and __iter__'
    def __init__(self, seqn):
        self.seqn = seqn
        self.i = 0
    def __next__(self):
        if self.i >= len(self.seqn): raise StopIteration
        v = self.seqn[self.i]
        self.i += 1
        return v

class N:
    'Iterator missing __next__()'
    def __init__(self, seqn):
        self.seqn = seqn
        self.i = 0
    def __iter__(self):
        return self

class E:
    'Test propagation of exceptions'
    def __init__(self, seqn):
        self.seqn = seqn
        self.i = 0
    def __iter__(self):
        return self
    def __next__(self):
        3 // 0

class S:
    'Test immediate stop'
    def __init__(self, seqn):
        pass
    def __iter__(self):
        return self
    def __next__(self):
        raise StopIteration

def L(seqn):
    'Test multiple tiers of iterators'
    return chain(map(lambda x:x, R(Ig(G(seqn)))))


class TestVariousIteratorArgs(unittest.TestCase):
    pass

    def test_accumulate(self):
        s = [1,2,3,4,5]
        r = [1,3,6,10,15]
        n = len(s)
        for g in (G, I, Ig, L, R):
            self.assertEqual(list(accumulate(g(s))), r)
        self.assertEqual(list(accumulate(S(s))), [])
        self.assertRaises(TypeError, accumulate, X(s))
        self.assertRaises(TypeError, accumulate, N(s))
        self.assertRaises(ZeroDivisionError, list, accumulate(E(s)))

    def test_chain(self):
        for s in ("123", "", range(1000), ('do', 1.2), range(2000,2200,5)):
            for g in (G, I, Ig, S, L, R):
                self.assertEqual(list(chain(g(s))), list(g(s)))
                self.assertEqual(list(chain(g(s), g(s))), list(g(s))+list(g(s)))
            self.assertRaises(TypeError, list, chain(X(s)))
            self.assertRaises(TypeError, list, chain(N(s)))
            self.assertRaises(ZeroDivisionError, list, chain(E(s)))

    def test_compress(self):
        for s in ("123", "", range(1000), ('do', 1.2), range(2000,2200,5)):
            n = len(s)
            for g in (G, I, Ig, S, L, R):
                self.assertEqual(list(compress(g(s), repeat(1))), list(g(s)))
            self.assertRaises(TypeError, compress, X(s), repeat(1))
            self.assertRaises(TypeError, compress, N(s), repeat(1))
            self.assertRaises(ZeroDivisionError, list, compress(E(s), repeat(1)))

    def test_product(self):
        for s in ("123", "", range(1000), ('do', 1.2), range(2000,2200,5)):
            self.assertRaises(TypeError, product, X(s))
            self.assertRaises(TypeError, product, N(s))
            self.assertRaises(ZeroDivisionError, product, E(s))

    def test_cycle(self):
        for s in ("123", "", range(1000), ('do', 1.2), range(2000,2200,5)):
            for g in (G, I, Ig, S, L, R):
                tgtlen = len(s) * 3
                expected = list(g(s))*3
                actual = list(islice(cycle(g(s)), tgtlen))
                self.assertEqual(actual, expected)
            self.assertRaises(TypeError, cycle, X(s))
            self.assertRaises(TypeError, cycle, N(s))
            self.assertRaises(ZeroDivisionError, list, cycle(E(s)))

    def test_groupby(self):
        for s in (range(10), range(0), range(1000), (7,11), range(2000,2200,5)):
            for g in (G, I, Ig, S, L, R):
                self.assertEqual([k for k, sb in groupby(g(s))], list(g(s)))
            self.assertRaises(TypeError, groupby, X(s))
            self.assertRaises(TypeError, groupby, N(s))
            self.assertRaises(ZeroDivisionError, list, groupby(E(s)))

    def test_filter(self):
        for s in (range(10), range(0), range(1000), (7,11), range(2000,2200,5)):
            for g in (G, I, Ig, S, L, R):
                self.assertEqual(list(filter(isEven, g(s))),
                                 [x for x in g(s) if isEven(x)])
            self.assertRaises(TypeError, filter, isEven, X(s))
            self.assertRaises(TypeError, filter, isEven, N(s))
            self.assertRaises(ZeroDivisionError, list, filter(isEven, E(s)))

    def test_filterfalse(self):
        for s in (range(10), range(0), range(1000), (7,11), range(2000,2200,5)):
            for g in (G, I, Ig, S, L, R):
                self.assertEqual(list(filterfalse(isEven, g(s))),
                                 [x for x in g(s) if isOdd(x)])
            self.assertRaises(TypeError, filterfalse, isEven, X(s))
            self.assertRaises(TypeError, filterfalse, isEven, N(s))
            self.assertRaises(ZeroDivisionError, list, filterfalse(isEven, E(s)))

    def test_zip(self):
        for s in ("123", "", range(1000), ('do', 1.2), range(2000,2200,5)):
            for g in (G, I, Ig, S, L, R):
                self.assertEqual(list(zip(g(s))), lzip(g(s)))
                self.assertEqual(list(zip(g(s), g(s))), lzip(g(s), g(s)))
            self.assertRaises(TypeError, zip, X(s))
            self.assertRaises(TypeError, zip, N(s))
            self.assertRaises(ZeroDivisionError, list, zip(E(s)))

    def test_ziplongest(self):
        for s in ("123", "", range(1000), ('do', 1.2), range(2000,2200,5)):
            for g in (G, I, Ig, S, L, R):
                self.assertEqual(list(zip_longest(g(s))), list(zip(g(s))))
                self.assertEqual(list(zip_longest(g(s), g(s))), list(zip(g(s), g(s))))
            self.assertRaises(TypeError, zip_longest, X(s))
            self.assertRaises(TypeError, zip_longest, N(s))
            self.assertRaises(ZeroDivisionError, list, zip_longest(E(s)))

    def test_map(self):
        for s in (range(10), range(0), range(100), (7,11), range(20,50,5)):
            for g in (G, I, Ig, S, L, R):
                self.assertEqual(list(map(onearg, g(s))),
                                 [onearg(x) for x in g(s)])
                self.assertEqual(list(map(operator.pow, g(s), g(s))),
                                 [x**x for x in g(s)])
            self.assertRaises(TypeError, map, onearg, X(s))
            self.assertRaises(TypeError, map, onearg, N(s))
            self.assertRaises(ZeroDivisionError, list, map(onearg, E(s)))

    def test_islice(self):
        for s in ("12345", "", range(1000), ('do', 1.2), range(2000,2200,5)):
            for g in (G, I, Ig, S, L, R):
                self.assertEqual(list(islice(g(s),1,None,2)), list(g(s))[1::2])
            self.assertRaises(TypeError, islice, X(s), 10)
            self.assertRaises(TypeError, islice, N(s), 10)
            self.assertRaises(ZeroDivisionError, list, islice(E(s), 10))

    def test_starmap(self):
        for s in (range(10), range(0), range(100), (7,11), range(20,50,5)):
            for g in (G, I, Ig, S, L, R):
                ss = lzip(s, s)
                self.assertEqual(list(starmap(operator.pow, g(ss))),
                                 [x**x for x in g(s)])
            self.assertRaises(TypeError, starmap, operator.pow, X(ss))
            self.assertRaises(TypeError, starmap, operator.pow, N(ss))
            self.assertRaises(ZeroDivisionError, list, starmap(operator.pow, E(ss)))

    def test_takewhile(self):
        for s in (range(10), range(0), range(1000), (7,11), range(2000,2200,5)):
            for g in (G, I, Ig, S, L, R):
                tgt = []
                for elem in g(s):
                    if not isEven(elem): break
                    tgt.append(elem)
                self.assertEqual(list(takewhile(isEven, g(s))), tgt)
            self.assertRaises(TypeError, takewhile, isEven, X(s))
            self.assertRaises(TypeError, takewhile, isEven, N(s))
            self.assertRaises(ZeroDivisionError, list, takewhile(isEven, E(s)))

    def test_dropwhile(self):
        for s in (range(10), range(0), range(1000), (7,11), range(2000,2200,5)):
            for g in (G, I, Ig, S, L, R):
                tgt = []
                for elem in g(s):
                    if not tgt and isOdd(elem): continue
                    tgt.append(elem)
                self.assertEqual(list(dropwhile(isOdd, g(s))), tgt)
            self.assertRaises(TypeError, dropwhile, isOdd, X(s))
            self.assertRaises(TypeError, dropwhile, isOdd, N(s))
            self.assertRaises(ZeroDivisionError, list, dropwhile(isOdd, E(s)))

#     def test_tee(self):
#         for s in ("123", "", range(1000), ('do', 1.2), range(2000,2200,5)):
#             for g in (G, I, Ig, S, L, R):
#                 it1, it2 = tee(g(s))
#                 self.assertEqual(list(it1), list(g(s)))
#                 self.assertEqual(list(it2), list(g(s)))
#             self.assertRaises(TypeError, tee, X(s))
#             self.assertRaises(TypeError, tee, N(s))
#             self.assertRaises(ZeroDivisionError, list, tee(E(s))[0])

# class LengthTransparency(unittest.TestCase):
#     pass

#     def test_repeat(self):
#         self.assertEqual(operator.length_hint(repeat(None, 50)), 50)
#         self.assertEqual(operator.length_hint(repeat(None, 0)), 0)
#         self.assertEqual(operator.length_hint(repeat(None), 12), 12)

#     def test_repeat_with_negative_times(self):
#         self.assertEqual(operator.length_hint(repeat(None, -1)), 0)
#         self.assertEqual(operator.length_hint(repeat(None, -2)), 0)
#         self.assertEqual(operator.length_hint(repeat(None, times=-1)), 0)
#         self.assertEqual(operator.length_hint(repeat(None, times=-2)), 0)

class RegressionTests(unittest.TestCase):

#     def test_sf_793826(self):
#         # Fix Armin Rigo's successful efforts to wreak havoc

#         def mutatingtuple(tuple1, f, tuple2):
#             # this builds a tuple t which is a copy of tuple1,
#             # then calls f(t), then mutates t to be equal to tuple2
#             # (needs len(tuple1) == len(tuple2)).
#             def g(value, first=[1]):
#                 if first:
#                     del first[:]
#                     f(next(z))
#                 return value
#             items = list(tuple2)
#             items[1:1] = list(tuple1)
#             gen = map(g, items)
#             z = zip(*[gen]*len(tuple1))
#             next(z)

#         def f(t):
#             global T
#             T = t
#             first[:] = list(T)

#         first = []
#         mutatingtuple((1,2,3), f, (4,5,6))
#         second = list(T)
#         self.assertEqual(first, second)


    def test_sf_950057(self):
        # Make sure that chain() and cycle() catch exceptions immediately
        # rather than when shifting between input sources

        def gen1():
            hist.append(0)
            yield 1
            hist.append(1)
            raise AssertionError
            hist.append(2)

        def gen2(x):
            hist.append(3)
            yield 2
            hist.append(4)

        hist = []
        self.assertRaises(AssertionError, list, chain(gen1(), gen2(False)))
        self.assertEqual(hist, [0,1])

        hist = []
        self.assertRaises(AssertionError, list, chain(gen1(), gen2(True)))
        self.assertEqual(hist, [0,1])

        hist = []
        self.assertRaises(AssertionError, list, cycle(gen1()))
        self.assertEqual(hist, [0,1])

    def test_long_chain_of_empty_iterables(self):
        # Make sure itertools.chain doesn't run into recursion limits when
        # dealing with long chains of empty iterables. Even with a high
        # number this would probably only fail in Py_DEBUG mode.
        it = chain.from_iterable(() for unused in range(100000))  
        self.assertRaises(StopIteration, next, it)

#     def test_issue30347_1(self):
#         def f(n):
#             if n == 5:
#                 list(b)
#             return n != 6
#         for (k, b) in groupby(range(10), f):
#             list(b)  # shouldn't crash

#     def test_issue30347_2(self):
#         class K:
#             def __init__(self, v):
#                 pass
#             def __eq__(self, other):
#                 nonlocal i
#                 i += 1
#                 if i == 1:
#                     next(g, None)
#                 return True
#         i = 0
#         g = next(groupby(range(10), K))[1]
#         for j in range(2):
#             next(g, None)  # shouldn't crash


# class SubclassWithKwargsTest(unittest.TestCase):
#     def test_keywords_in_subclass(self):
#         # count is not subclassable...
#         for cls in (repeat, zip, filter, filterfalse, chain, map,
#                     starmap, islice, takewhile, dropwhile, cycle, compress):
#             class Subclass(cls):
#                 def __init__(self, newarg=None, *args):
#                     cls.__init__(self, *args)
#             try:
#                 Subclass(newarg=1)
#             except TypeError as err:
#                 # we expect type errors because of wrong argument count
#                 self.assertNotIn("keyword arguments", err.args[0])

# @support.cpython_only
# class SizeofTest(unittest.TestCase):
#     def setUp(self):
#         self.ssize_t = struct.calcsize('n')

#     check_sizeof = support.check_sizeof

#     def test_product_sizeof(self):
#         basesize = support.calcobjsize('3Pi')
#         check = self.check_sizeof
#         check(product('ab', '12'), basesize + 2 * self.ssize_t)
#         check(product(*(('abc',) * 10)), basesize + 10 * self.ssize_t)

#     def test_combinations_sizeof(self):
#         basesize = support.calcobjsize('3Pni')
#         check = self.check_sizeof
#         check(combinations('abcd', 3), basesize + 3 * self.ssize_t)
#         check(combinations(range(10), 4), basesize + 4 * self.ssize_t)

#     def test_combinations_with_replacement_sizeof(self):
#         cwr = combinations_with_replacement
#         basesize = support.calcobjsize('3Pni')
#         check = self.check_sizeof
#         check(cwr('abcd', 3), basesize + 3 * self.ssize_t)
#         check(cwr(range(10), 4), basesize + 4 * self.ssize_t)

#     def test_permutations_sizeof(self):
#         basesize = support.calcobjsize('4Pni')
#         check = self.check_sizeof
#         check(permutations('abcd'),
#               basesize + 4 * self.ssize_t + 4 * self.ssize_t)
#         check(permutations('abcd', 3),
#               basesize + 4 * self.ssize_t + 3 * self.ssize_t)
#         check(permutations('abcde', 3),
#               basesize + 5 * self.ssize_t + 3 * self.ssize_t)
#         check(permutations(range(10), 4),
#               basesize + 10 * self.ssize_t + 4 * self.ssize_t)


# libreftest = """ Doctest for examples in the library reference: libitertools.tex
# >>> amounts = [120.15, 764.05, 823.14]
# >>> for checknum, amount in zip(count(1200), amounts):
# ...     print('Check %d is for $%.2f' % (checknum, amount))
# ...
# Check 1200 is for $120.15
# Check 1201 is for $764.05
# Check 1202 is for $823.14
# >>> import operator
# >>> for cube in map(operator.pow, range(1,4), repeat(3)):
# ...    print(cube)
# ...
# 1
# 8
# 27
# >>> reportlines = ['EuroPython', 'Roster', '', 'alex', '', 'laura', '', 'martin', '', 'walter', '', 'samuele']
# >>> for name in islice(reportlines, 3, None, 2):
# ...    print(name.title())
# ...
# Alex
# Laura
# Martin
# Walter
# Samuele
# >>> from operator import itemgetter
# >>> d = dict(a=1, b=2, c=1, d=2, e=1, f=2, g=3)
# >>> di = sorted(sorted(d.items()), key=itemgetter(1))
# >>> for k, g in groupby(di, itemgetter(1)):
# ...     print(k, list(map(itemgetter(0), g)))
# ...
# 1 ['a', 'c', 'e']
# 2 ['b', 'd', 'f']
# 3 ['g']
# # Find runs of consecutive numbers using groupby.  The key to the solution
# # is differencing with a range so that consecutive numbers all appear in
# # same group.
# >>> data = [ 1,  4,5,6, 10, 15,16,17,18, 22, 25,26,27,28]
# >>> for k, g in groupby(enumerate(data), lambda t:t[0]-t[1]):
# ...     print(list(map(operator.itemgetter(1), g)))
# ...
# [1]
# [4, 5, 6]
# [10]
# [15, 16, 17, 18]
# [22]
# [25, 26, 27, 28]
# >>> def take(n, iterable):
# ...     "Return first n items of the iterable as a list"
# ...     return list(islice(iterable, n))
# >>> def prepend(value, iterator):
# ...     "Prepend a single value in front of an iterator"
# ...     # prepend(1, [2, 3, 4]) -> 1 2 3 4
# ...     return chain([value], iterator)
# >>> def enumerate(iterable, start=0):
# ...     return zip(count(start), iterable)
# >>> def tabulate(function, start=0):
# ...     "Return function(0), function(1), ..."
# ...     return map(function, count(start))
# >>> import collections
# >>> def consume(iterator, n=None):
# ...     "Advance the iterator n-steps ahead. If n is None, consume entirely."
# ...     # Use functions that consume iterators at C speed.
# ...     if n is None:
# ...         # feed the entire iterator into a zero-length deque
# ...         collections.deque(iterator, maxlen=0)
# ...     else:
# ...         # advance to the empty slice starting at position n
# ...         next(islice(iterator, n, n), None)
# >>> def nth(iterable, n, default=None):
# ...     "Returns the nth item or a default value"
# ...     return next(islice(iterable, n, None), default)
# >>> def all_equal(iterable):
# ...     "Returns True if all the elements are equal to each other"
# ...     g = groupby(iterable)
# ...     return next(g, True) and not next(g, False)
# >>> def quantify(iterable, pred=bool):
# ...     "Count how many times the predicate is true"
# ...     return sum(map(pred, iterable))
# >>> def padnone(iterable):
# ...     "Returns the sequence elements and then returns None indefinitely"
# ...     return chain(iterable, repeat(None))
# >>> def ncycles(iterable, n):
# ...     "Returns the sequence elements n times"
# ...     return chain(*repeat(iterable, n))
# >>> def dotproduct(vec1, vec2):
# ...     return sum(map(operator.mul, vec1, vec2))
# >>> def flatten(listOfLists):
# ...     return list(chain.from_iterable(listOfLists))
# >>> def repeatfunc(func, times=None, *args):
# ...     "Repeat calls to func with specified arguments."
# ...     "   Example:  repeatfunc(random.random)"
# ...     if times is None:
# ...         return starmap(func, repeat(args))
# ...     else:
# ...         return starmap(func, repeat(args, times))
# >>> def pairwise(iterable):
# ...     "s -> (s0,s1), (s1,s2), (s2, s3), ..."
# ...     a, b = tee(iterable)
# ...     try:
# ...         next(b)
# ...     except StopIteration:
# ...         pass
# ...     return zip(a, b)
# >>> def grouper(n, iterable, fillvalue=None):
# ...     "grouper(3, 'ABCDEFG', 'x') --> ABC DEF Gxx"
# ...     args = [iter(iterable)] * n
# ...     return zip_longest(*args, fillvalue=fillvalue)
# >>> def roundrobin(*iterables):
# ...     "roundrobin('ABC', 'D', 'EF') --> A D E B F C"
# ...     # Recipe credited to George Sakkis
# ...     pending = len(iterables)
# ...     nexts = cycle(iter(it).__next__ for it in iterables)
# ...     while pending:
# ...         try:
# ...             for next in nexts:
# ...                 yield next()
# ...         except StopIteration:
# ...             pending -= 1
# ...             nexts = cycle(islice(nexts, pending))
# >>> def powerset(iterable):
# ...     "powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)"
# ...     s = list(iterable)
# ...     return chain.from_iterable(combinations(s, r) for r in range(len(s)+1))
# >>> def unique_everseen(iterable, key=None):
# ...     "List unique elements, preserving order. Remember all elements ever seen."
# ...     # unique_everseen('AAAABBBCCDAABBB') --> A B C D
# ...     # unique_everseen('ABBCcAD', str.lower) --> A B C D
# ...     seen = set()
# ...     seen_add = seen.add
# ...     if key is None:
# ...         for element in iterable:
# ...             if element not in seen:
# ...                 seen_add(element)
# ...                 yield element
# ...     else:
# ...         for element in iterable:
# ...             k = key(element)
# ...             if k not in seen:
# ...                 seen_add(k)
# ...                 yield element
# >>> def unique_justseen(iterable, key=None):
# ...     "List unique elements, preserving order. Remember only the element just seen."
# ...     # unique_justseen('AAAABBBCCDAABBB') --> A B C D A B
# ...     # unique_justseen('ABBCcAD', str.lower) --> A B C A D
# ...     return map(next, map(itemgetter(1), groupby(iterable, key)))
# >>> def first_true(iterable, default=False, pred=None):
# ...     '''Returns the first true value in the iterable.
# ...
# ...     If no true value is found, returns *default*
# ...
# ...     If *pred* is not None, returns the first item
# ...     for which pred(item) is true.
# ...
# ...     '''
# ...     # first_true([a,b,c], x) --> a or b or c or x
# ...     # first_true([a,b], x, f) --> a if f(a) else b if f(b) else x
# ...     return next(filter(pred, iterable), default)
# >>> def nth_combination(iterable, r, index):
# ...     'Equivalent to list(combinations(iterable, r))[index]'
# ...     pool = tuple(iterable)
# ...     n = len(pool)
# ...     if r < 0 or r > n:
# ...         raise ValueError
# ...     c = 1
# ...     k = min(r, n-r)
# ...     for i in range(1, k+1):
# ...         c = c * (n - k + i) // i
# ...     if index < 0:
# ...         index += c
# ...     if index < 0 or index >= c:
# ...         raise IndexError
# ...     result = []
# ...     while r:
# ...         c, n, r = c*r//n, n-1, r-1
# ...         while index >= c:
# ...             index -= c
# ...             c, n = c*(n-r)//n, n-1
# ...         result.append(pool[-1-n])
# ...     return tuple(result)
# This is not part of the examples but it tests to make sure the definitions
# perform as purported.
# >>> take(10, count())
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
# >>> list(prepend(1, [2, 3, 4]))
# [1, 2, 3, 4]
# >>> list(enumerate('abc'))
# [(0, 'a'), (1, 'b'), (2, 'c')]
# >>> list(islice(tabulate(lambda x: 2*x), 4))
# [0, 2, 4, 6]
# >>> it = iter(range(10))
# >>> consume(it, 3)
# >>> next(it)
# 3
# >>> consume(it)
# >>> next(it, 'Done')
# 'Done'
# >>> nth('abcde', 3)
# 'd'
# >>> nth('abcde', 9) is None
# True
# >>> [all_equal(s) for s in ('', 'A', 'AAAA', 'AAAB', 'AAABA')]
# [True, True, True, False, False]
# >>> quantify(range(99), lambda x: x%2==0)
# 50
# >>> a = [[1, 2, 3], [4, 5, 6]]
# >>> flatten(a)
# [1, 2, 3, 4, 5, 6]
# >>> list(repeatfunc(pow, 5, 2, 3))
# [8, 8, 8, 8, 8]
# >>> import random
# >>> take(5, map(int, repeatfunc(random.random)))
# [0, 0, 0, 0, 0]
# >>> list(pairwise('abcd'))
# [('a', 'b'), ('b', 'c'), ('c', 'd')]
# >>> list(pairwise([]))
# []
# >>> list(pairwise('a'))
# []
# >>> list(islice(padnone('abc'), 0, 6))
# ['a', 'b', 'c', None, None, None]
# >>> list(ncycles('abc', 3))
# ['a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c']
# >>> dotproduct([1,2,3], [4,5,6])
# 32
# >>> list(grouper(3, 'abcdefg', 'x'))
# [('a', 'b', 'c'), ('d', 'e', 'f'), ('g', 'x', 'x')]
# >>> list(roundrobin('abc', 'd', 'ef'))
# ['a', 'd', 'e', 'b', 'f', 'c']
# >>> list(powerset([1,2,3]))
# [(), (1,), (2,), (3,), (1, 2), (1, 3), (2, 3), (1, 2, 3)]
# >>> all(len(list(powerset(range(n)))) == 2**n for n in range(18))
# True
# >>> list(powerset('abcde')) == sorted(sorted(set(powerset('abcde'))), key=len)
# True
# >>> list(unique_everseen('AAAABBBCCDAABBB'))
# ['A', 'B', 'C', 'D']
# >>> list(unique_everseen('ABBCcAD', str.lower))
# ['A', 'B', 'C', 'D']
# >>> list(unique_justseen('AAAABBBCCDAABBB'))
# ['A', 'B', 'C', 'D', 'A', 'B']
# >>> list(unique_justseen('ABBCcAD', str.lower))
# ['A', 'B', 'C', 'A', 'D']
# >>> first_true('ABC0DEF1', '9', str.isdigit)
# '0'
# >>> population = 'ABCDEFGH'
# >>> for r in range(len(population) + 1):
# ...     seq = list(combinations(population, r))
# ...     for i in range(len(seq)):
# ...         assert nth_combination(population, r, i) == seq[i]
# ...     for i in range(-len(seq), 0):
# ...         assert nth_combination(population, r, i) == seq[i]
# """

# __test__ = {'libreftest' : libreftest}

# def test_main(verbose=None):
#     # test_classes = (TestBasicOps, TestVariousIteratorArgs, TestGC,
#     #                 RegressionTests, LengthTransparency,
#     #                 SubclassWithKwargsTest, TestExamples,
#     #                 TestPurePythonRoughEquivalents,
#     #                 SizeofTest)

#     # verify reference counting
#     if verbose and hasattr(sys, "gettotalrefcount"):
#         import gc
#         counts = [None] * 5
#         for i in range(len(counts)):
#             support.run_unittest(*test_classes)
#             gc.collect()
#             counts[i] = sys.gettotalrefcount()
#         print(counts)

#     # doctest the examples in the library reference
#     support.run_doctest(sys.modules[__name__], verbose)

if __name__ == "__main__":
    # test_main(verbose=True)
     unittest.main()